Concept Design for the Arroyo del Valle Realignment at Lake Bnps.acgov.org/nps-assets/docs/npstri.pdf · 172-square-mile Arroyo del Valle basin is located upstream of Del Valle Reservoir,

Concept Design for the Arroyo del Valle

Realignment at Lake B Prepared for

CEMEX, Inc. El iot Mine Alameda County, Cal i forn ia

July 18, 2016

701 Pike Street, Suite 1200

Seattle, WA 98101

Concept Design for the Arroyo del Valle Realignment at Lake B

Prepared for CEMEX, Inc. El iot Mine

Alameda County, Cal i forn ia July 18, 2016

Nathan H. Foged

Cal i fo rn ia Ci v i l Eng inee r C66395, Exp. June 2018 Enginee r in Respons ib le Charge

i

CEMEX AdVR Concept Design 20160718.docx

Table of Contents List of Figures .............................................................................................................................................. iii

List of Tables ............................................................................................................................................... iv

List of Abbreviations .................................................................................................................................... v

Executive Summary ............................................................................................................................... ES-1 Hydrology ...................................................................................................................................... ES-2 Geomorphology .............................................................................................................................. ES-3 Conceptual Design Development .................................................................................................. ES-4 Recommendations for Further Study ............................................................................................ ES-9

1. Introduction .......................................................................................................................................1-1 2. Design Objectives ..............................................................................................................................2-1 3. Hydrology ...........................................................................................................................................3-1

3.1 Watershed Description ...........................................................................................................3-1 3.2 Streamflow Analysis................................................................................................................3-2

Flow Duration and Distribution ................................................................................3-3 Peak Flow Frequency ...............................................................................................3-5

4. Geomorphology .................................................................................................................................4-1 4.1 Pre-Developed Conditions ......................................................................................................4-1 4.2 Anthropogenic Changes .........................................................................................................4-2

Watershed and Floodplain Development ...............................................................4-2 Construction of Del Valle Reservoir .........................................................................4-3

4.3 Assessment of Existing Conditions ........................................................................................4-4 Arroyo del Valle at Lake B ........................................................................................4-4 Arroyo del Valle at Lake A ........................................................................................4-5 Arroyo del Valle at Sycamore Grove Park ................................................................4-6 Signs of Degradation and Instability .......................................................................4-7

4.4 Considerations for Restoration ..............................................................................................4-8 Pattern and Planform ...............................................................................................4-8 Design Discharges ....................................................................................................4-9 Hydraulic Geometry ............................................................................................... 4-10 Slope and Sinuosity ............................................................................................... 4-11 Alluvial Material ..................................................................................................... 4-12

5. Conceptual Design ............................................................................................................................5-1 5.1 Hydraulic Design .....................................................................................................................5-2

Cross-Section ............................................................................................................5-2 Channel Pattern ........................................................................................................5-3 Bed and Bend Variation ...........................................................................................5-6

Table of Contents Conceptual Design of Arroyo Del Valle Realignment at Lake B

ii CEMEX AdVR Concept Design 20160718.docx

5.2 Stability Analysis .....................................................................................................................5-8 Calculating Sediment Loads ....................................................................................5-9 Balancing Sediment Loads ................................................................................... 5-11

5.3 Formulating the Design Concept ........................................................................................ 5-14 Tributaries .............................................................................................................. 5-14 Transitions ............................................................................................................. 5-15 Additional Features ............................................................................................... 5-16

6. Conclusions and Recommendations ...............................................................................................6-1 7. Limitations .........................................................................................................................................7-1 8. References ........................................................................................................................................8-1

Appendix A: Conceptual Design Drawings ............................................................................................... A-1

Appendix B: Additional Flow Data ........................................................................................................... B-1

Appendix C: Bulletin 17B Approach .........................................................................................................C-1

Appendix D: Initial Geomorphic Assessment .......................................................................................... D-1

Appendix E: Field Data .............................................................................................................................. E-1

Appendix F: Infiltration Testing ................................................................................................................. F-1

Appendix G: Magnitude-Frequency Analysis .......................................................................................... G-1

Conceptual Design of Arroyo del Valle Realignment at Lake B Table of Contents

iii


List of Figures Figure ES-1. Eliot Facility vicinity and proposed realignment reach ................................................... ES-1

Figure ES-2. Pre-dam and post-dam flow duration curves calculated using average daily flows at AVL ................................................................................. ES-3

Figure ES-3. Sketch of a compound single-thread channel with low-flow, bankfull, and flood sections ................................................................................... ES-4

Figure ES-4. Reach-averaged cross-section widths for compound channel design .......................... ES-4

Figure ES-5. Typical morphological variations and bed forms within bends ...................................... ES-5

Figure ES-6. Typical morphological variations and bed forms within bends ...................................... ES-7

Figure ES-7. Schematic of bank tie-in at upstream transition ............................................................ ES-8

Figure 1. Eliot Facility vicinity and proposed realignment reach ...........................................................1-1

Figure 2. Project conceptual design development process ...................................................................2-3

Figure 3. Correlation of average daily discharge data at USGS gauges 11176500 (AVL) and 11176600 (AVP) ...............................................................................................................................3-2

Figure 4. Pre-dam and post-dam flow duration curves calculated using average daily flows at AVL ..3-3

Figure 5. Flow frequency histogram for AVL daily discharges ................................................................3-4

Figure 6. Average daily discharge data for AVL after the construction of Del Valle Reservoir .............3-5

Figure 7. Aerial photographs of Arroyo del Valle in Sycamore Grove Park ............................................4-4

Figure 8. Geomorphic observations along Arroyo del Valle at Lake B ...................................................4-5

Figure 9. Geomorphic observations along Arroyo del Valle at Lake A ...................................................4-6

Figure 10. Geomorphic observations along Arroyo del Valle in Sycamore Grove Park ........................4-7

Figure 11. Sketch of a compound single-thread channel with low-flow, bankfull, and flood sections4-9

Figure 12. Arroyo del Valle stream profiles and slope estimates ....................................................... 4-11

Figure 13. Proposed expansion of Lake B and new alignment .............................................................5-1

Figure 14. Reach-averaged cross-section widths for compound channel design ................................5-3

Figure 15. Meander and bend parameter definitions ............................................................................5-3

Figure 16. Example of a sine-generated meander pattern for λ = 407 and K = 1.13 .........................5-5

Figure 17. Meander pattern for bankfull channel ..................................................................................5-6

Figure 18. Cross-section showing secondary flow in bends...................................................................5-6

Figure 19. Typical morphological variations and bed forms within bends ............................................5-7

Figure 20. Relation between applied stress and frequency of occurrence in geomorphic processes5-10

Figure 21. Reaches of Arroyo del Valle used for sediment continuity analysis ................................. 5-11

Figure 22. Average annual sediment load transported through Arroyo del Valle reaches ............... 5-12

Figure 23. Cumulative sediment loading curves ................................................................................. 5-13


iv CEMEX AdVR Concept Design 20160718.docx

Figure 24. Conceptual design overview ................................................................................................ 5-14

Figure 25. Schematic of bank tie-in at upstream transition ............................................................... 5-15

List of Tables Table ES-1. Summary of Design Parameters ....................................................................................... ES-6

Table 2. Arroyo del Valle Realignment Design Objectives and Criteria .................................................2-2

Table 3. Exceedance Flows for Arroyo del Valle ......................................................................................3-3

Table 4. Peak Discharge Frequency from Regression Analysis .............................................................3-5

Table 5. Bankfull Dimensions Calculated for Cross-Sections in Sycamore Grove Park .................... 4-10

Conceptual Design of Arroyo del Valle Realignment at Lake B Table of Contents

v


List of Abbreviations ACCDA Alameda County Community

Development Agency

Amendment SMP-23 Reclamation Plan Amendment

AVL Arroyo del Valle at Livermore

AVP Arroyo del Valle at Pleasanton

Balance Balance Hydrologics

BC Brown and Caldwell

Caltrans California Department of Transportation

CCCST Central California Coast steelhead trout

CDFW California Department of Fish and Wildlife

CEMEX CEMEX Construction Materials, Inc.

CEQA California Environmental Quality Act

cfs cubic foot/feet per second

DEM digital elevation model

FEMA Federal Emergency Management Agency

FIS Flood Insurance Study

ft foot/feet

ft/ft foot/feet vertical per 1 foot horizontal

ft/s foot/feet per second

ft2 square foot/feet

H:V horizontal:vertical

IACWD Interagency Advisory Committee on Water Data

KANE KANE GeoTech, Inc.

LiDAR light detecting and ranging

LP3 log-Pearson Type III

LSA LSA Associates

mm millimeter(s)

msl mean sea level

NMFS National Marine Fisheries Service

Project Arroyo del Valle Realignment Project

RWQCB Regional Water Quality Control Board

SFEI San Francisco Estuary Institute

SGP Sycamore Grove Park

SMP Surface Mining Permit

Spinardi Spinardi Associates

SR 84 State Route 84

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

Valley Livermore-Amador Valley

Zone 7 Zone 7 Water Agency


vi CEMEX AdVR Concept Design 20160718.docx

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ES-1


Executive Summary CEMEX Construction Materials, Inc. (CEMEX) owns and operates the Eliot Facility, a sand and gravel mining operation located between the cities of Pleasanton and Livermore within the unincorporated area of Alameda County, California. CEMEX is seeking to amend the reclamation plan for the Eliot Facility. Option 1 of the Surface Mining Permit (SMP) 23 Reclamation Plan Amendment (Amendment)—submitted to the Alameda County Community Development Agency (ACCDA) in August 2014—proposes to move Arroyo del Valle south to a new stream alignment, allowing for expansion of the Lake B mining area. At the same time, CEMEX will restore and enhance the Arroyo del Valle corridor to create a complex and varied aquatic habitat for vertebrates and native plant species (see Figure ES-1). This proposed project is henceforth referred to as the Project.

Figure ES-1. Eliot Facility vicinity and proposed realignment reach

Preliminary correspondence with regulatory agencies, particularly the Regional Water Quality Control Board (RWQCB), has identified needs for an assessment of the geomorphic conditions of Arroyo del Valle and preliminary design evaluations to confirm that the realigned channel will be stable and persist, while still providing the natural form and function needed to support fish and native habitats. Thus, the primary goals of the Project are to allow for expansion of Lake B mining, while enhancing the riparian and aquatic habitat along Arroyo del Valle. In response to these concerns, CEMEX contracted with Brown and Caldwell (BC) and Balance Hydrologics (Balance) to evaluate the

Executive Summary Conceptual Design for Arroyo del Valle Realignment at Lake B

ES-2 CEMEX AdVR Concept Design 20160718.docx

geomorphic conditions of Arroyo del Valle and develop a concept-level design for the Project. BC began by defining the following specific design objectives: • Establish a new stream corridor (channel and floodplain) that is located outside of Lake B mining

operations • Design transitions that conform to existing grade at upstream and downstream tie-in points

using gradual and stable transitions • Provide flood conveyance with sufficient capacity to avoid adverse flooding impacts and/or

substantive increases in flood risk to adjacent properties and infrastructure • Stabilize banks to minimize the risk of channel migration/avulsion that could threaten adjacent

structures or cause the stream to be captured by Lake B, or flow into adjacent areas • Evaluate long-term channel stability and minimize the risk of long-term channel degradation that

could result in channel incision, bank steepening/failures, substantial downstream sediment deposition, and/or upstream instability

• Create a fluvial stream system that generates natural geomorphic conditions and maintains a stable yet dynamic equilibrium within the context of overall watershed conditions

• Create new riparian and aquatic habitat areas as part of a natural ecosystem that supports native flora and fauna

• Avoid barriers to fish migration and create fluvial formations and natural habitat features that allow for fish passage

BC performed preliminary hydrologic and geomorphic investigations to support the development of a conceptual design for the Project.

Hydrology Arroyo del Valle is located in the upper Alameda Creek watershed. Approximately 85 percent of the 172-square-mile Arroyo del Valle basin is located upstream of Del Valle Reservoir, which was constructed in 1968. Del Valle Reservoir has altered the hydrologic flow regime in the lower reaches of Arroyo del Valle, dramatically decreasing the flood flows and providing sustained releases during the dry season (Kamman 2009). Altered flows have also contributed to changes in the Arroyo del Valle channel; the once actively braided channel network along the valley floor now has shifted to a more defined central channel system (Kamman 2009). The pre-dam and post-dam flow duration curves in Figure ES-2 show a reduction in large discharges and a change from intermittent to perennial flow in Arroyo del Valle.

Conceptual Design for Arroyo del Valle Realignment at Lake B Executive Summary

ES-3


Figure ES-2. Pre-dam and post-dam flow duration curves calculated using average daily flows at AVL

Geomorphology Arroyo del Valle was historically a wide braided stream that transported large amounts of coarse sediment from its headwaters in the Diablo Range to the wide flat valley floor (SFEI 2013). Arroyo del Valle is a highly modified system because of nearly 2 centuries of development (i.e., grazing, agriculture, urbanization, floodplain channelization, and gravel mining) and the construction of Del Valle Reservoir in 1968. Sand and gravel mining has occurred along the Arroyo del Valle alluvial formations since the late 1800s, including the areas around the Eliot Facility.

Given this dynamic setting, there is no single absolute size and configuration for a restored reach of Arroyo del Valle. Channel restoration design efforts for Arroyo del Valle should focus on establishing a suitable range of channel geometries that will allow for some adjustment over time to accommodate the flow and sediment regime it will experience.

Preliminary geomorphic investigations suggest that a single-thread morphology would be suitable for restoring the Arroyo del Valle channel along the new alignment. While there are some indicators that it could also function as a braided system similar to its historical condition, the historical flow regime and sediment loads have been dramatically altered by the construction of Del Valle Dam and the arroyo appears to have shifted from braided to a single-thread form in the Sycamore Grove Park area. Moreover, the Project will be constructed through a developed area where spatial constraints limit the flexibility of the design to incorporate a more dynamic pattern. Therefore, initial design evaluations will focus on a single-thread channel, with potential for adding complexity such as a floodplain overflow channel during later design stages. Assuming a single-thread morphology, Balance recommends a compound-channel design with a low-flow channel, intermediate or bankfull channel, and floodplain corridor (Figure ES-3, below).

0.01

0.10

1.00

10.00

100.00

1,000.00

10,000.00

0% 20% 40% 60% 80% 100%

Dis

chrg

e (c

fs)

Percent Time Exceeded

Pre-dam (1912-1967)

Post-dam (1969-2015)



Figure ES-3. Sketch of a compound single-thread channel with low-flow, bankfull, and flood sections

The low-flow channel should be designed to convey a discharge of around 9 to 10 cubic feet per second (cfs) in a concentrated channel to support aquatic habitat and maintain flow depths and velocities for fish passage during critical periods when discharges may be low. The bankfull channel should be designed to convey the estimated channel-forming discharge of 216 cfs. The floodplain should be designed to convey the 100-year peak discharge of 7,000 cfs as defined by the Federal Emergency Management Agency (FEMA).

Existing topography and aerial photography indicate that Arroyo del Valle currently has an average bed slope of approximately 0.56 percent between Island Pond (just downstream of the Project site) to the base of Del Valle Dam. The sinuosity of this same reach ranges between about 1.05 and 1.15 feet vertical per 1 foot horizontal (ft/ft).

Conceptual Design Development BC developed a conceptual design for a single-thread compound channel with low-flow, bankfull, and flood stages. Given the site constraints and the findings from the preliminary geomorphic assessment, BC performed hydraulic design calculations and a sediment continuity-based stability analysis to develop design parameters such as channel widths, depths, slope, and sinuosity. To a large extent, these analyses were informed by the conditions observed upstream in Sycamore Grove Park. Figure ES-4 illustrates the general cross-section dimensions and Figure ES-5 illustrates how that cross-section will vary through bends and pool-riffle patterns. Table ES-1 provides a summary of the conceptual design parameters.

Figure ES-4. Reach-averaged cross-section widths for compound channel design

36 ft

10 ft

100-year water surface

Bankfull

Low flow

215 ft

260 ft

3

1

2:1


ES-5


Figure ES-5. Typical morphological variations and bed forms within bends

Adapted from Copeland 2001; Harmon et al. 2012 Not drawn to scale

Bank erosion

A

A’

C

C’

B

B’

D Dp

Da

Wi Wp

A A’ B B’

Wa

C C’

Thalweg

Riffle Point bar

Pool

PoolRiffle

PoolRiffle

ThalwegLp

SECTION A-A’ SECTION B-B’

SECTION C-C’

PROFILE

PLAN

PoolRiffle

D

Wa

Da

Dp

Wi

Wp

Lp = pool-pool length= depth at cross-over= depth at pool= depth at bend apex= width at pool

= width at bend apex= width at cross-over



Table ES-1. Summary of Design Parameters

Concept Component Design parameter Symbol Units Value C

ompo

und

chan

nel c

ross

-sec

tion

Floodplain corridor Top width Wf ft 260

Bottom width Bf ft 215

Side slope Zf H:V 3:1

Longitudinal slope Sf ft/ft 0.0056

Sinuosity Kf ft/ft 1.00

Design discharge for flood conveyance Q100 cfs 7,000

Freeboard for containing flood Fb ft 3.0

Bankfull channel Top width Wb ft 36

Bottom width Bb ft 28

Side slope Zb H:V 2:1

Maximum depth (including low-flow channel) Di ft 2.1

Mean depth (including low-flow channel) Dm ft 1.56

Cross-sectional area Ab ft2 56

Longitudinal slope Sb ft/ft 0.0053

Sinuosity Kb ft/ft 1.05–1.10

Bankfull/channel-forming discharge Qb cfs 216

Low-flow channel Top width Wl ft 10

Bottom width Bl ft 8

Depth Dl ft 0.5

Side slope Zl H:V 2:1

Longitudinal slope Sl ft/ft 0.0051

Sinuosity Kl ft/ft 1.05–1.15

Patt

ern

and

plan

form

Meander Belt Floodplain width (terrace measured from toe of slope) Wfp ft 215

Meander belt to floodplain buffer width Wbuffer ft 30

Meander belt width (floodplain terrace minus buffer) Wmeander ft 185

Meander amplitude α ft 149

Meander width ratio (Wmeander/Wbf) WRmeander None 5.1

Meander wavelength λ ft 700–800

Pool-riffle sequence Depth ratio (Dmax/Dmean) DR ft 2.27

Maximum pool depth Dmax ft 3.5

Pool offset ratio POR None 0.36

Pool offset from bend apex POA ft 65

Pool width Wpool ft 52

The hydraulic design parameters summarized in Table ES-1 were applied to the site to form a complete design concept. Figure ES-6 provides an overview of the proposed realigned channel. Appendix A provides a concept-level drawing set with a plan and profile of the proposed alignment.


ES-7


Figure ES-6. Typical morphological variations and bed forms within bends

The realigned channel begins about 1,600 feet downstream of Isabel Avenue at an elevation of roughly 393 feet above msl. The new alignment briefly parallels the existing channel and then shifts southwest closer to Vineyard Avenue. Construction of the new channel and floodplain corridor will eliminate an existing remnant lake at the southern edge of the site and restore an uninterrupted stream channel. The downstream end of the realigned channel will tie back into the existing channel several hundred feet northwest of the future extent of Lake B at an elevation of roughly 358 feet above msl. The realigned corridor extends roughly 5,800 linear feet and the realigned bankfull channel within the floodplain extends approximately 6,200 linear feet.

Tributaries. Topographic mapping, aerial photos, and onsite observations indicate that at least two, and possibly three, significant tributaries flow into Arroyo del Valle between the proposed upstream and downstream tie-in points. The drainage areas for these tributaries range between about 0.5 to 2 square miles. It is recommended that these be incorporated into the design to create controlled and stable confluences with the proposed new channel.

Transitions. Transitions at the upstream and downstream points will need to be designed to reduce the potential for an avulsion that could allow the stream to abandon the new alignment. The banks of the new bankfull channel and the side slope of the floodplain should be reinforced and stabilized using natural features such as those described in the California Salmonid Stream Habitat Restoration Manual (Flosi et al. 2010). These could include live vegetated crib walls, native material revetments, log wing-deflectors, and tree revetments. The banks of the new channel should be extended and tied into the outer slopes of the existing floodplain to intercept flow from a wider area



and minimize the potential for Arroyo del Valle to shift channels upstream and flank the transition point. This concept is illustrated in Figure ES-7.

Figure ES-7. Schematic of bank tie-in at upstream transition

The transition at the downstream end of the realignment can be allowed to flow more freely. The channel banks and floodplain side slopes can simply be graded to provide a smooth and gradual transition back into the existing geometry.

Additional Features. Given the considerable uncertainty associated with transient and highly variable phenomena such as sediment loads, transport rates, and equilibrium dynamics, BC recommends that additional features be added to the design to help mitigate disturbances that could lead to severe degradation or channel widening. Such design provisions might be avoided if the realigned corridor was extremely wide and unconfined, where unexpected or extreme shifts in the channel might go unnoticed. However, the Project site is located in a developed area, bounded by Vineyard Avenue to the south and Lake B to the north, as well as utilities and other infrastructure in the vicinity. Therefore, as the design progresses, natural features that offer increased stability should be added, particularly to vulnerable areas such as the outsides of bends. These types of features offer a dual purpose by both promoting a stable channel configuration and providing a more reliable platform for ecological restoration as plant communities are established and fish-passable features are created. As cited previously, documents such as the California Salmonid Stream Habitat Restoration Manual (Flosi et al. 2010) provide a variety of alternatives for habitat improvements, fish passage, and bank stabilization techniques.

Existing floodplain

Proposed thalwegRelic channel/flowpathExisting low-flow channel

Proposed stabilized banks

L E G E N D


ES-9


Recommendations for Further Study Given the considerable uncertainty associated with sediment loads, transport estimates, and equilibrium dynamics, BC recommends that additional features be added to the design to help mitigate disturbances that could lead to severe degradation or channel widening. These features and similar improvements should be investigated as the design progresses. The following bullets summarize BC’s recommendations for further study: • Evaluate the use of natural features such as rock weirs/vanes for bed and bank stabilization to

help mitigate disturbances that could trigger degradation or channel widening. • Coordinate with Alameda County and other relevant permitting agencies to apprise them of the

latest design concept and begin to elicit feedback on the conceptual design. Relevant permitting agencies could include California Fish and Game (California Code Sections 1601/1603- Streambed Alteration Agreement), U.S. Army Corps of Engineers (USACE) (Section 404 of the Clean Water Act), California Regional Water Quality Control Board (RWQCB) (Section 401 of the Clean Water Act), and National Marine Fisheries Service (NMFS) for potential impacts to federally listed species.

• The Alameda Creek watershed is listed as one of the eight anchor watersheds in the San Francisco Estuary that support the federally listed threatened Central California Coast steelhead trout (CCCST). While there are currently barriers to fish passage downstream of the Project site, fish passage may still become a key objective for the Project. Additional studies will need to be conducted and the design will need to be refined to accommodate specific fish habitat and passage criteria.

• Arroyo del Valle is a highly disturbed system. Findings from the initial geomorphic assessment support the design concept; however, this is not a static system and conditions continue to change over time. Additional investigations are in process to inform the final design.

• Continue to develop the Project toward full design documentation for construction. The design approach and submittal stages will depend on CEMEX’s preferred method for construction. For example, if the entire Project goes out to competitive bid, CEMEX may want to develop a full bid package with detailed plans and specifications. Or, if preferred, CEMEX could consider an alternative delivery method in which the design documents are less detailed, but the engineer is more involved with the construction.




1-1


Section 1

Introduction CEMEX Construction Materials, Inc. (CEMEX) owns and operates the Eliot Facility, a sand and gravel mining operation located between the cities of Pleasanton and Livermore within the unincorporated area of Alameda County, California. CEMEX is seeking approval of an amendment to its existing Reclamation Plan, which was originally approved in 1987 under Surface Mining Permit (SMP) 23.

In 2014, Mitchell Chadwick and Spinardi Associates prepared the SMP-23 Reclamation Plan Amendment (Amendment) and submitted it to the Alameda County Community Development Agency (ACCDA). The Amendment presents options for mining Lake B to an elevation of 150 feet above mean sea level (msl). Under the preferred Option 1, CEMEX proposes to move Arroyo del Valle south along a new alignment parallel to Vineyard Avenue to allow for expansion of Lake B. At the same time, CEMEX will restore and enhance the Arroyo del Valle corridor to create a complex and varied aquatic habitat for vertebrates and native plant species (see Figure 1).

Figure 1. Eliot Facility vicinity and proposed realignment reach

Section 1 Conceptual Design for Arroyo del Valle Realignment at Lake B

1-2 CEMEX AdVR Concept Design 20160718.docx

In 2015, Alameda County issued a Notice of Preparation of a draft environmental impact report for the Amendment in accordance with the California Environmental Quality Act (CEQA). Preliminary discussions on environmental issues with the California Regional Water Quality Control Board (RWQCB), U.S. Army Corps of Engineers (USACE), and California Department of Fish and Wildlife (CDFW) have prompted CEMEX to conduct investigations and prepare a draft conceptual design document for the Arroyo del Valle Realignment Project (Project). The agencies, particularly RWQCB, would like to see an assessment of the geomorphic conditions of Arroyo del Valle and additional design evaluations to confirm that the realigned channel will be stable and persist, while still providing the natural form and function needed to support fish and native habitats. In a letter to ACCDA, the water resource control engineer at the San Francisco Bay RWQCB provided the following comments:

To facilitate extracting aggregate from the southern portion of SMP-23, CEMEX is proposing to realign Arroyo Del Valle to the south of its current alignment by creating a new channel that runs closer to Vineyard Avenue. The revised reclamation plan will attempt to create a new creek channel that provides improved habitat over the current channel alignment. The creation of a new stable creek channel is a complex process that requires the participation of experienced fluvial geomorphologists to determine creek widths, creek depths, creek thalweg1 gradients, and creek sinuosity that are in equilibrium with the hydrology of the watershed and the topography of the watershed.

The description of channel realignment in the Draft EIR should include creek widths, creek depths, creek thalweg gradients, and creek sinuosity for the new channel alignment so that reviewers can assess the likelihood that the new channel will be in equilibrium with its watershed.

In order to minimize the risk of channel incisement, the active channel of the creek should be connected to a floodplain set at the elevation of the channel forming flow event. The channel forming flow event is usually a flow event between the 1-year and 2-year event, with rural watersheds having channel forming flows closer to the 2-year event and urbanized watersheds having channel forming flows closer to the 1-year event. According to the discussion of Arroyo Del Valle realignment and enhancement on page B-6 of the NOP, a berm is to be constructed along the south side of Lake A to prevent Lake A from being inundated by flow in Arroyo Del Valle during a 100-year event. This berm should be constructed sufficiently distant from the active channel of Arroyo Del Vale to allow the establishment of an appropriately sized floodplain at the channel forming flow level in Arroyo Del Valle. Without the creation of an appropriately positioned floodplain, the new channel of Arroyo Del Valle is likely to incise, and such incision will damage riparian habitat along the creek bank and compromise habitat integrity within the new channel alignment (Wines 2015).

In response to these inquiries, CEMEX contracted with Brown and Caldwell (BC) and Balance Hydrologics (Balance) to evaluate the geomorphic conditions of Arroyo del Valle and develop a concept-level design for the Project. The resulting study achieved the following objectives: • Collect data and observations at the Project site and upstream areas, including estimates of

existing, relict bed material gradation and typical channel dimensions

1 The thalweg is the line connecting the points of lowest bed elevation in a river or stream channel.

Conceptual Design for Arroyo del Valle Realignment at Lake B Section 1

1-3


• Characterize the existing/baseline geomorphic conditions of Arroyo del Valle including a preliminary assessment of the channel stability and fluvial geomorphology within the context of the regulated flows downstream of Del Valle Reservoir

• Develop preliminary design recommendations for a restored channel and floodplain corridor along the proposed new alignment including forms and features that promote an active yet dynamically stable stream channel

• Prepare concept-level drawings illustrating the proposed alignment and basic channel design features

This report summarizes the results of the study and provides conceptual design drawings for the proposed Project. Design information contained in this document is considered preliminary and will be revised as the design continues to develop and progress toward construction.




2-1


Section 2

Design Objectives The primary goals of the Project are to allow for expansion of Lake B mining, while enhancing the riparian and aquatic habitat along Arroyo del Valle. Given these goals, BC has defined the following design objectives for the proposed Project: • Realignment: establish a new stream corridor (channel and floodplain) outside of Lake B mining

operations • Transitions: conform to existing grade at upstream and downstream tie-in points using gradual

and stable transitions • Flood conveyance: avoid adverse flooding impacts and/or substantive increases in flood risk to

adjacent properties and infrastructure • Erosion and bank stability: minimize the risk of channel migration/avulsion that could threaten

adjacent structures or cause the stream to be captured by Lake B, or flow into adjacent areas • Long-term channel stability: minimize the risk of long-term channel degradation that could result

in channel incision, bank steepening/failures, substantial downstream sediment deposition, and/or upstream instability

• Geomorphic function: create a fluvial stream system that generates natural geomorphic conditions and maintains a stable yet dynamic equilibrium within the context of overall watershed conditions

• Riparian and aquatic habitat: create new habitat areas as part of a natural ecosystem that support native flora and fauna

• Fish passage: avoid barriers to fish migration and create fluvial formations and natural habitat features that allow for fish passage

Table 2 below lists the design objectives along with corresponding design criteria for the Project.



Table 2. Arroyo del Valle Realignment Design Objectives and Criteria

Issue Design objective Design criteria

Spatial constraints

Establish a new stream corridor (channel and floodplain) outside of Lake B mining operations

Preliminary grading by Spinardi suggests that a corridor width of approximately 260 feet can be created between Lake B and Vineyard Avenue (Mitchell Chadwick and Spinardi Associates, 2014).

Conform to existing grade at upstream and downstream tie-in points using gradual and stable transitions

The channel bed elevation should match existing upstream and downstream tie-in locations; the average longitudinal slope of the corridor should be equal to the predominant valley slope of approximately 0.56%.

Flood conveyance

Avoid adverse flooding impacts and/or substantive increases in flood risk to adjacent properties and infrastructure

The regulatory flood hazard area as defined by FEMA is based on the area inundated by the 1% annual chance event, or the 100-year flood event. According to the current effective flood insurance study, the 100-year peak discharge on Arroyo del Valle downstream of Del Valle Dam is 7,000 cfs.

The new stream corridor should contain the 100-year flood without increasing upstream inundation areas. Given the uncertainty in peak discharge estimates and floodplain hydraulics, a minimum freeboard height of 3 feet will be assumed for preliminary design as a factor of safety, which is consistent with Federal requirements for riverine levees.

Channel stability

Minimize the risk of channel migration/avulsion that could threaten adjacent structures or cause the stream to be captured by Lake B, or flow into adjacent areas

Water surface elevations corresponding to a 100-year peak discharge plus 3 feet of freeboard should not exceed lateral roadway/berm elevations, thereby preventing water from flowing directly from the floodplain into Lake B or other adjacent depressions.

Minimize the risk of long-term channel degradation that could result in channel incision, bank steepening/failures, substantial downstream sediment deposition, and/or upstream instability

Develop a channel configuration (dimensions, pattern, and profile) that maintains a balanced sediment transport regime through the Project reach.

Incorporate a compound channel design to convey typical low flows, bankfull or channel-forming flows, and flood flows while maintaining connectivity between the channel and floodplain.

Flood flows in excess of the channel-forming discharge should spill into a floodplain such that the flow is unconfined, resulting in lower overbank velocities and shear stresses.

Geomorphic function

Create a fluvial stream system that generates natural geomorphic conditions and maintains a stable yet dynamic equilibrium within the context of the overall watershed

The dimension, pattern, and profile of the restored channel should be designed to transport sediment at rates that create a long-term balance with the inflowing sediment load.

Fill materials used to construct the channel and floodplain should be comparable to the existing stream bed material with a bed competence and composition sufficient to limit degradation.

Biological resources

Create new riparian and aquatic habitat areas as part of a natural ecosystem that supports native flora and fauna

Construct a low-flow channel that can be used to create habitat areas such as freshwater marsh, perennial stream, and intermittent stream.

Construct an intermediate, frequently flooded channel that can be used to create habitat areas such as riparian scrub and riparian wetland.

Construct a floodplain that can be used to create riparian habitat areas that are flooded only occasionally.

Avoid barriers to fish migration and create fluvial formations and natural habitat features that allow for fish passage

The low-flow channel should be configured to maintain targeted flow depths and velocity ranges for identified fish species and life stages.

In-channel features should not create obstructions or depth/velocity conditions that exceed specified criteria for identified fish species and life stages.


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Preliminary investigations were performed to evaluate Project design criteria and support design development. These investigations can be broadly divided into four categories: civil/site design, hydrology, geomorphology, and biology. The flow chart in Figure 2 describes the major steps and illustrates how these investigations feed into the overall conceptual design development. This report focuses mostly on the hydrologic and geomorphic investigations supporting the design (see Sections 3 and 4, respectively). Section 5 describes the development of the conceptual design including hydraulic design and stability analyses.

Figure 2. Project conceptual design development process

Design Objectives

Check corridor alignment with grading and spatial constraints

Overlay proposed mining with existing base mapping data

Hydrology

Collect and review historical streamflow data at USGS gauges

Develop pre-and post-dam series and perform flow duration analysis

BiologyGeomorphology

Develop peak annual flow series and perform flow frequency analysis

Perform field investigations and

collect channel data

Analyze channel data and assess the current geomorphic conditions

Conduct brief review of historical data and aerial photography

Civil/Site

Develop plan/profile drawings showing

transitions and features

Identify mitigation requirements

Develop landscape and native planting

recommendations

Conduct biological surveys

Channel stability assessment

Natural channel dimensions

Target channel morphology

Morphological variability

Bendway sectionsPool offset Pool scour depth

Low-flow width/depthBankfull width/depth

Grade controlBank protection

Flow duration curvesFlow frequency curves

Reach-averagecross-section

Detailed Design(Phase 2)

Plan and profile

Hydraulic design variations

Channel stabilitydesign

Corridor alignmentCorridor widthCorridor profile

Bed sediment sizeHydraulic geometryPattern and profilePlanform

SinuosityMeanders

Habitat types Bench heights

Plantings and mitigation




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Section 3

Hydrology Arroyo del Valle is located in the upper Alameda Creek watershed. The arroyo2 drains an area of approximately 172 square miles before it discharges to Arroyo de la Laguna west of Pleasanton. Arroyo de la Laguna flows south and discharges into Alameda Creek near the town of Sunol. Alameda Creek then flows west through the East Bay Hills before discharging into San Francisco Bay.

3.1 Watershed Description Approximately 85 percent (146 square miles) of the Arroyo del Valle basin is located upstream of Del Valle Reservoir. The watershed above Del Valle Dam comprises steep-sloped canyons composed primarily of hard sedimentary and metasedimentary rocks with small areas of basic igneous rocks (Welch et al. 1966).

The dam was constructed in 1968 with a reservoir capacity of approximately 77,100 acre-feet to serve as off-channel storage for water delivered through the South Bay Aqueduct (part of the California State Water project) and for flood control. Zone 7 Water Agency (Zone 7)—one of three water agencies served by the South Bay Aqueduct—uses Del Valle Reservoir for water supply storage, and reserves a small portion of its capacity to store runoff from the local watershed.

Del Valle Reservoir has altered the hydrologic flow regime in the lower reaches of Arroyo del Valle (Kamman 2009). Peak flows have decreased and large-magnitude flood flows have been virtually eliminated. Managed releases during the dry season have resulted in perennial flow conditions along the valley floor rather than the historical intermittent flow conditions when the arroyo would become dry in the summertime (Kamman 2009; LSA 2013). Altered flows have also contributed to changes in the Arroyo del Valle channel; the once actively braided channel network along the valley floor now has shifted to a more defined central channel system (Kamman 2009).

Directly downstream of the dam, Arroyo del Valle flows through a narrow, sinuous canyon until it reaches the valley floor about 1 mile downstream, near the Veterans Administration hospital. From there, Arroyo del Valle flows approximately 2 miles through Sycamore Grove Park, which is an important community park that preserves mature Western Sycamore trees along this reach of the historical Arroyo del Valle floodplain.

CEMEX’s Eliot Facility is located northwest of Sycamore Grove Park, just downstream from the Vallecitos Road crossing. Arroyo del Valle flows along the southern portion of the Eliot Facility site adjacent to the Lake A and Lake B mining areas. The arroyo flows through the site for approximately 3 miles before flowing into Island Pond at the northwest edge of the site. The arroyo flows through Boris Lake along the south side of the Shadow Cliffs Regional Recreation Area and then continues west through the city of Pleasanton.

Several small streams drain into Arroyo del Valle between the dam and its confluence with Arroyo de la Laguna. BC used available topographic data to delineate drainage areas and found that roughly

2 An arroyo is a stream or a watercourse and is generally characterized by steep terrain and intermittent or ephemeral flow; arroyos are typically associated with arid regions such as southwestern U.S. The terms “arroyo” and “stream” are used interchangeably throughout this report.



17 square miles drain to Arroyo del Valle between the dam and the downstream boundary of the site.

3.2 Streamflow Analysis Streamflow data records are available for two U.S. Geological Survey (USGS) stream-gauging stations on Arroyo del Valle: • USGS 111176500 Arroyo del Valle at Livermore (AVL): average daily discharge available from

1912 to present; located just downstream of Del Valle Reservoir and upstream of the Study Reach

• USGS 111176600 Arroyo del Valle at Pleasanton (AVP): average daily discharge available from 1957–86; located just downstream of Main Street in the city of Pleasanton and downstream of the Study Reach

Figure 3 shows a correlation comparison of the average daily discharge data for each of the USGS stream gauges. Construction of Del Valle Reservoir in 1968 substantially altered the hydrologic flow regime (i.e., frequency and duration of stream flows) in Arroyo del Valle; therefore, BC used streamflow data only from 1968 onward for this analysis (Kamman 2009). Concurrent data ranging from 1968–85 show a high level of correlation (i.e., R-squared = 0.96), likely because of the dominance of regulated flow releases from Del Valle Reservoir. Given the close correlation among the two gauges, BC was able to narrow the hydrologic analyses to just data from the AVL gauge, which has a substantially longer period of record and data available through the present.

Figure 3. Correlation of average daily discharge data at USGS gauges

11176500 (AVL) and 11176600 (AVP)

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Flow Duration and Distribution BC divided the mean daily discharge time series for AVL into two periods: • Pre-dam data (i.e., before the construction of Del Valle Reservoir) span from 1912–67; however,

records are not available from 1930–57, so the time series covers 28 water years • Post-dam data span from 1969 to 2015 for a period covering 46 water years

BC calculated flow duration curves using the mean daily flow data for the pre-dam and post-dam periods (Figure 4).

Figure 4. Pre-dam and post-dam flow duration curves calculated using average daily flows at AVL

Figure 4 indicates that the construction of Del Valle Reservoir resulted in a reduction in high flows and an increase in low flows, as would be expected for a regulated system. Moreover, the comparison of flow duration curves shows that Arroyo del Valle shifted from intermittent to perennial flow conditions. Table 3 lists specific flow exceedances for percentiles of interest, based on commonly used criteria for fish passage evaluations (Taylor and Love 2010).

Table 3. Exceedance Flows for Arroyo del Valle

Percent time exceeded Stream flow (cfs)

Pre-dam (1912–67) Post-dam (1969–2015) 1 719 485 5 111 47

10 40 28 50 0.23 1.12 90 — a 0.23 95 — a 0.15

a. Pre-dam streamflow data at AVL indicate that the arroyo was dry 43% of the time.

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Another way to analyze streamflow data is to create a distribution histogram. BC used 100 logarithmically distributed flow bins to generate flow distribution histograms for pre-dam and post-dam conditions (Figure 5).

Figure 5. Flow frequency histogram for AVL daily discharges

Figure 5 indicates that, with the construction of Del Valle Reservoir, flows in Arroyo del Valle shifted to a bimodal distribution with a typical wet season baseflow around 0.5 cubic foot per second (cfs) and a dry season flow release around 10 cfs. For additional information on the seasonal variation of streamflow in Arroyo del Valle, refer to Appendix B for plots of monthly mean and median daily discharges.

BC visually examined the post-dam average daily discharge data for the AVL gauge and found that the 14 most recent water years—2002–15—exhibit a reasonably consistent pattern of seasonal flow releases (Figure 6, below). During this time, the average daily discharge was 9.4 cfs, which is roughly equivalent to the 10.0 cfs dry season flow observed in the post-dam flow histogram (Figure 5).

02468

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Figure 6. Average daily discharge data for AVL after the construction of Del Valle Reservoir

Peak Flow Frequency BC used the peak annual discharge data for AVL to perform a statistical regression analysis using the standard Bulletin 17B method recommended by the Interagency Advisory Committee on Water Data (IACWD) (IACWD 1982). Details regarding the Bulletin 17B method and BC’s assumptions are provided in Appendix C. Table 4 lists the estimated peak discharges for a range of annual probabilities. The peak discharge frequency results are also plotted in Figure, below.

Table 4. Peak Discharge Frequency from Regression Analysis

Recurrence interval (years)

Annual chance of exceedance

Peak discharge (cfs) Pre-dam Post-dam

1.5 66.7% 547 95

2.0 50.0% 1,413 216

5.0 20.0% 6,434 969

10.0 10.0% 12,087 2,010

25.0 4.0% 21,198 4,200

50.0 2.0% 28,818 6,616

100.0 1.0% 36,695 9,816

200.0 0.5% 44,565 13,921

500.0 0.2% 54,617 20,954

a. Based on data from USGS 111176500 (pre-dam, 1912–67) and (post-dam, 1969–2015) b. Peak discharges calculated using Bulletin 17B methodology (see Appendix C) c. According to the Federal Emergency Management Agency’s (FEMA) current Flood

Insurance Study (FIS) for Alameda County, the peak 100-year discharge for Arroyo del Valle is 7,000 cfs (FEMA 2011), which corresponds to a managed flood release from the dam (USACE 1978). The published discharge of 7,000 cfs is regarded as a better estimate for floodplain management because it accounts for the flood storage at Del Valle Reservoir.

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Section 4

Geomorphology The Livermore-Amador Valley (Valley) is a wide depression in the Diablo Range, bounded by the East Bay Hills to the west and the Altamont Hills to the east. The western portion is composed of the Amador Valley and includes the city of Pleasanton. The eastern portion is composed of the Livermore Valley and includes the city of Livermore. The two valleys together form the Valley.

According to the San Francisco Estuary Institute (SFEI), the Valley was formed by geological processes and provides a wide space for streams to spread and sink (SFEI 2013). Numerous streams that drain out of the surrounding hills have deposited sediments during thousands of years and have filled the Valley (SFEI 2013).

Arroyo Mocho and Arroyo del Valle are two major streams draining into the southern portion of the Valley. Historically, these were wide-braided streams that deposited large amounts of coarse sediment transported from their headwaters in the Diablo Range (SFEI 2013). Sand and gravel mining has occurred along the Arroyo Mocho and Arroyo del Valle alluvial formations since the late 1800s, including the areas around the Eliot Facility. Geology maps by Helley and Graymer indicate that gravel extraction in this area occurs in relict stream channels and Holocene alluvium3 (Helley and Graymer 1997).

4.1 Pre-Developed Conditions The Alameda Creek Watershed Historical Ecology Study published by SFEI synthesizes historical information from numerous sources to describe conditions in the Alameda Creek watershed prior to significant Euro-American modification (SFEI 2013). The section on Arroyo del Valle describes an alluvial system along the Valley that transitioned from a narrow confined channel as it exited the upper canyon, to a wide-braided system along the valley floor, and then back to a single thread before bifurcating into multiple distributary channels as it entered into the Pleasanton Marsh complex. The following excerpt from the SFEI study describes the observed geomorphology:

Del Valle began to split into multiple channels shortly after entering the valley, approximately where the Veteran’s Hospital is located today. Historical maps show Arroyo del Valle broadening to develop a braided pattern, with clearly depicted islands between the multiple channels of the creek (Boardman 1870, Duerr 1872a, Allardt 1874, Gibbes 1878, Thompson and West 1878, USGS 1906) [. . .] In the braided reach of the creek, the riparian corridor may have been up to 1,500 feet wide. In some places, even wider outer relic floodplain terraces are still visible in the LiDAR survey and historical aerials, extending the potential corridor width up to 3,000 feet [. . .] In contrast to the braided reach, the portion of Del Valle in the vicinity of Pleasanton was a single-thread meandering channel (Boardman 1870, Allardt 1874, Thompson and West 1878, USGS 1906). Historically, this lower reach began in what is now Shadow Cliffs Regional Recreational Area, where the dominant

3 Alluvium is unconsolidated terrestrial sediment composed of sorted or unsorted sand, gravel, silt, and clay that has been deposited by flowing water. Historically, sediments from upper canyons and mountainous areas were transported into the wide flat Livermore-Amador Valley, where the stream energy dissipated and sediments were deposited over riverbeds, lakes, and alluvial fans.



substrate shifted from gravel to clay (mapped as fine-grained Livermore silty fine sandy loam; Westover and Van Duyne 1910). By this point, the stream had dropped its load of coarse gravels on its fan and lost most surface flow (SFEI 2013).

The SFEI study goes on to describe Arroyo del Valle as a historically intermittent stream (SFEI 2013). As the stream lost power, coarse gravels deposited over an alluvial fan and surface flow began to percolate into the coarse sediments. The following excerpt from the SFEI study describes the coarse material formations and loss of surface flows:

This braided form corresponded with a coarse gravelly substrate and large sediment load; through much of Livermore Valley the strip of soil underlying the creek was characterized in the historical soil survey by “numerous abandoned channels,” an underlying “bed of coarse gravel many feet in thickness,” and in the contemporary soil survey as “porous sandy soil,” or “riverwash” (Westover and Van Duyne 1910:35, Welch et al. 1966). Water sank through these gravels, so that much of the flow of the creek continued subsurface [. . .] Through this reach, Del Valle shifted from a perennial to an intermittent stream. At the edge of the valley, a mile downstream of the reservoir, Sherman Day noted “a fine stream of water, running over a dam of sandstone rocks” in August 1853 (Day 1853:289). Another mile and a half downstream, in Sycamore Grove Park, he described water “in pools.” As water continued to sink through the gravels, he found “no water in summer” at Isabel Avenue, another two miles further downstream (1853). The pools were part of the gradual transition as water sank further below the surface (SFEI 2013).

4.2 Anthropogenic Changes Human disturbances in a watershed and floodplain development can affect flow, conveyance, and the balance of sediment supply, which can often lead to fluvial disturbances that result in channel degradation (Schum et al. 1984; Simon and Rinaldi 2006). Arroyo del Valle is a highly modified system because of nearly 2 centuries of development (i.e., grazing, agriculture, urbanization, floodplain channelization, and gravel mining) and the construction of Del Valle Reservoir in 1968.

Watershed and Floodplain Development This section summarizes types of watershed and floodplain development in the Valley.

Grazing. Settlers in the early to mid-1800s began modifying the land by grazing cattle, clearing trees for firewood, and diverting water for irrigation and drainage (SFEI 2013). By the mid-1800s cattle and sheep grazing was widespread and was likely to have begun changing the ecological and morphological processes within the watershed (SFEI 2013). Grazing not only changes vegetative cover, but also compacts soil, hastens erosion, and contributes to stream degradation and channel widening (Meehan and Platts 1978).

Agriculture. The Valley began to shift from ranching to agriculture in the middle to late 1800s (SFEI 2013). Although grains were the primary crop in the Valley, settlers also planted grapes, orchard trees, and some row crops (SFEI 2013). Around the turn of the century and into the mid-1900s, agricultural lands shifted from primarily dryland wheat farming to more irrigated farming with orchards, vineyards, and row crops (Clark 1915; McCann and Hinkel 1937; SFEI 2013). With increasing need for irrigation and drainage in the Valley, many streams were rerouted, straightened, channelized, and connected.

Urbanization. In the middle to late 20th century the Valley experienced rapid population growth and is now home to well over 200,000 people. Extensive urbanization in and around the cities of Livermore and Pleasanton have replaced open lands with residential and commercial developments


4-3


and new roadways. Most of the large valley wetlands have been drained and floodplains have continued to be narrowed and channelized. In many areas, the species composition of the remaining grasslands and riparian corridors has shifted toward non-native plant species (SFEI 2013). Runoff from newly paved (impermeable) surfaces increases stormwater flows, which has been shown to contribute to stream degradation and channel incision (Booth 1990; Bledsoe and Watson 2001).

Mining. The coarse gravelly formations underlying Arroyo Mocho and Arroyo del Valle have supported gravel mining and development in the region for nearly 150 years. There is evidence that—in addition to grazing and agriculture—gravel mining in the middle to late 1800s began to cause a shift in the course of Arroyo del Valle. SFEI compares historical maps from the 1870s to a USGS topographic quadrangle map from 1906, showing how the channel appears to have been narrowed and straightened over time (SFEI 2013). In-channel mining throughout much the 20th century continued to alter the channel and floodplain. Collins and Dunne examined a number of in-channel gravel mining case studies and found that mining activities considerably alter river morphology and habitat, and often interrupt the supply of gravel to downstream reaches (Collins and Dunne 1990).

Construction of Del Valle Reservoir As discussed in Section 3, the construction of Del Valle Reservoir had a substantial impact on the flow regime of Arroyo del Valle below the dam; peak flood flows were dramatically reduced and the duration of low flows were increased such that the stream shifted from intermittent to perennial. The dam has also had tremendous impact on the sediment regime in Arroyo del Valle by disrupting the natural transport of sediment from the upper watershed to the Valley. Using a standard relationship developed by Brune, BC estimated that roughly 97 percent of sediment flowing into Del Valle Reservoir would be trapped behind the dam (Brune 1953). The trapping and removal of sediment supply creates a clear water or sediment-starved condition downstream from the dam, which leads to channel degradation, bank erosion, and bed-coarsening (Williams and Wolman 1984; Kondolf and Matthews 1991). Williams and Wolman also found that riparian vegetation commonly increased in reaches downstream from the dams, likely because of the reduction in peak flows that would typically scour the riparian corridor (Williams and Wolman 1984).

In a study of Sycamore Grove Park, Kamman found that after 1968 sedimentation inputs to the Sycamore Grove Park reach are “likely derived solely from the reworking of [existing] channel [materials] between the Park and dam and inputs from the Dry Creek drainage, which enters the central portion of the Park from the north” (Kamman 2009). Kamman describes how the reduced sediment supply diminished gravel bar formation, lessened topographic variation, and coarsened/armored the channel bed to the point where it became dominated by gravel- and cobble-size material (Kamman 2009). According to Kamman, aerial photographs indicate an active braided-channel system as late as 1963, followed by photographs from the 1970s to the 1990s showing a drastic reduction in secondary channels and areas of floodplain disturbance, accompanied by vegetation encroachment across the floodplain and along the channel (Kamman 2009). A similar comparison is shown in Figure 7, below.



1958 (10 years before construction of Del Valle Reservoir) 2012 (44 years after construction of Del Valle Reservoir)

Figure 7. Aerial photographs of Arroyo del Valle in Sycamore Grove Park

4.3 Assessment of Existing Conditions Geomorphologists from Balance Hydrologics, Inc. (Balance) conducted three site visits and collected data in October 2015 to assist with their geomorphic assessment of Arroyo del Valle. Their findings are summarized in a draft technical memorandum on the initial geomorphic assessment (see Appendix D). The investigations focused on three reaches of Arroyo del Valle: • Adjacent to Lake B from the west end of the Eliot Facility site to Isabel Avenue • Adjacent to Lake A from Isabel Avenue to Vallecitos Road • Sycamore Grove Park

The Balance team (Bill Christner, Chelsea Neill, and Eric Donaldson) measured channel substrate and constructed particle size distributions from data collected at locations along Lake B, using standard Wolman pebble count methods and a reach-averaged procedure taken within the active channel. Balance also measured approximate channel dimensions using field tape measurements, and estimated bankfull dimensions at each location based on channel morphology. Additional discussion on bankfull channel dimensions is provided in Section 4.5.

Sections 4.3.1 through 4.3.3, below, contain observations and geomorphic descriptions from Balance’s assessments as summarized by Bill Christner (Balance 2016).

Arroyo del Valle at Lake B The riparian corridor along Arroyo del Valle near Lake B has thick vegetation that limits access to the active channel and also encroaches well into the active channel. In many areas this vegetation appears to be the dominant control of channel roughness. Shrub encroachment is likely a result of sustained summer releases from Del Valle Dam. Under drier, pre-dam conditions, the impenetrable growth was not present (Figure 7). Observations were made at three sites along this reach (see observation points 1, 2, and 3 in Figure 8 below).


4-5


Figure 8. Geomorphic observations along Arroyo del Valle at Lake B

Channel substrates at observation points 1 and 3 consisted of large cobbles and gravels covered with a veneer of fine silts and sands mixed with organics. Observation point 2 is located off-channel to the north of the main channel and is interpreted as a relict, abandoned channel that likely formed under pre-dam hydrologic conditions. Channel substrate at observation point 2 was composed of sands, gravels, and cobbles. Pebble counts and gradations curves for observation points 1 and 3 are provided in Appendix E along with cross-section plots showing estimated bankfull widths.

Arroyo del Valle at Lake A The Arroyo del Valle channel running along Lake A is also thickly vegetated but does provide areas of channel access. Riparian vegetation also encroaches well into the active channel throughout this reach. This reach is highly altered and was only investigated at a cursory level for the purposes of this preliminary geomorphic assessment.

Observations were made at three locations along the Lake A reach (see observation points 4, 5, and 6 in Figure 9, below). Although channel substrate was not directly measured, it was visually assessed and consisted of coarse sand to medium gravels in the area with active channel flow, and fine silts and sands along the channel margins where vegetation encroaching into the channel slows channel velocities and traps sediment. While no pebble counts were taken, cross-section dimensions were estimated with field tapes and the extent of vegetative encroachment was noted (see Appendix E).



Figure 9. Geomorphic observations along Arroyo del Valle at Lake A

Arroyo del Valle at Sycamore Grove Park Sycamore Grove Park is located immediately upstream of the Eliot Facility on the southeast side of Vallecitos Road. Walking trails within the park are set back from the arroyo on both banks; however, there is a footbridge and two wet crossings within the park. The footbridge is located approximately 2,000 feet upstream of Vallecitos Road. Olivina Trail Crossing is located about 1.0 mile upstream of Vallecitos Road and Kingfisher Crossing is nearly 1.5 miles upstream of Vallecitos Road. A South Bay Aqueduct outfall pipe is located on the left bank (looking downstream) immediately downstream of the Kingfisher Crossing. Balance estimated a discharge of 10 cfs from the pipe, which, at the time of the visit, appeared to be the sole source of flow in Arroyo del Valle.

Sycamore Grove Park contains relict, braided-channel morphology, attributed to geomorphic processes that were operating prior to the construction of Del Valle Dam. While multiple channels are present in Sycamore Grove Park, flows are presently restricted to a single thread. Channel access was not inhibited by vegetation, and vegetation did not appear to influence channel roughness and morphology as it did along Arroyo del Valle at the Eliot Facility. After performing an initial visual survey of Arroyo del Valle in Sycamore Grove Park, Balance identified four sites for data collection (Figure 10, below).


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Figure 10. Geomorphic observations along Arroyo del Valle in Sycamore Grove Park

Observation points 7 and 8 were located at riffles, while observation points 9 and 10 were collected at pools. Pebble counts and gradations curves for observation points 7 through 10 are provided in Appendix E. Appendix E also contains field-surveyed cross-section plots showing estimated bankfull widths at each location.

Signs of Degradation and Instability As discussed in Section 4.2, development and disturbance within the Arroyo del Valle watershed have likely destabilized and degraded the stream system over time. Simon and Hupp developed a channel evolution model to describe how destabilized and degrading streams change over time (Simon and Hupp 1986). As degrading streams become deeper and more incised, the main channel becomes disconnected from the floodplain and banks become steep and unstable. As steep banks are undermined mass wasting occurs, which begins to widen the channel. As degradation continues to migrate upstream, the now flatter bed slope cannot transport the incoming sediment and secondary aggradation begins to fill in the channel, leading to meandering and further widening.

During its site visit in October 2015, Balance observed some continuing signs of instability along the Sycamore Grove Park reach of Arroyo del Valle. Specifically, a high right bank with vertical exposure of roughly 12 to 15 feet could be seen immediately upstream from the lower pedestrian bridge in Sycamore Grove Park just south of the parking lot off Wetmore Road. The impacted reach begins approximately 120 feet downstream of the pedestrian bridge and continues upstream for roughly 450 feet. Such areas of channel destabilization could indicate that the channel is in a state of disequilibrium and may still be adjusting to changes in the watershed (Balance 2016).



Balance also examined the Isabel Avenue crossing, which has recently been graded and armored with riprap, forming a convex channel slope as it flows under the bridge. Vegetation throughout the area had recently been removed, including several small- to medium-sized trees along the channel banks, allowing easy access to the channel on both banks. The riprap blanket covers approximately 420 feet of channel bank to bank (Balance 2016).

These modifications are likely countermeasures to protect the bridge from scour. A report by WRECO described the bridge as “scour critical” because of past channel degradation that has reduced the cover over pier and abutment footings (WRECO 2009). It should also be noted that the scour analysis by WRECO assumes the channel has stabilized and that future bed degradation will be “negligible” (WRECO 2009).

WRECO’s assumptions are based on bridge inspections conducted by the California Department of Transportation (Caltrans). Caltrans inspected the Isabel Avenue/State Route 84 (SR 84) bridge at Arroyo del Valle on September 17, 2008. According to the Bridge Inspection Report, the channel degraded 6 feet between 1983 and 1999, but then stabilized. Although the Bridge Inspection Report attributed the degradation to in-stream gravel mining, it seems likely that there were multiple contributing factors, and that the arroyo may still be adjusting to the construction of Del Valle Dam. In a study of 21 dams constructed on alluvial rivers, Williams and Wolman found that most degradation occurred during the first 1 to 2 decades after a dam was completed (Williams and Wolman 1984).

4.4 Considerations for Restoration Arroyo del Valle is a highly modified fluvial system that has been altered and channelized, and the hydrologic and sediment regimes dramatically changed by the construction of Del Valle Reservoir. It is likely that the stream is still adjusting to these impacts and continued land use changes. While the degradation caused by the dam has likely diminished, there is still risk of instability and continued channel evolution. In addition, channels adjust naturally to episodic events such as watershed-scale wildfires and floods (Balance 2016).

Given this dynamic setting, there is no single absolute size and configuration for a restored reach of Arroyo del Valle. Channel restoration design efforts for Arroyo del Valle should focus on establishing a suitable range of channel geometries that will allow for some adjustment over time to accommodate the flow and sediment regime it will experience (Balance 2016).

Pattern and Planform Preliminary geomorphic investigations suggest that a single-thread morphology would be suitable for restoring the Arroyo del Valle channel along the new alignment (Bill Christner, personal communications, January 27, 2016). While there are some indicators that it could also function as a braided system similar to its historical condition, the historical flow regime and sediment loads have been dramatically altered by the construction of Del Valle Dam and the arroyo appears to have shifted from braided to a single-thread form in the Sycamore Grove Park area (Balance 2016). Moreover, the Project will be constructed through a developed area where spatial constraints limit the flexibility of the design to incorporate a more dynamic pattern. Therefore, initial design evaluations will focus on a single-thread channel, with potential for adding complexity such as a floodplain overflow channel during later design stages. Assuming a single-thread morphology, Balance recommends a compound-channel design with a low-flow channel, intermediate or bankfull channel, and a floodplain corridor (Figure 11, below).


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Figure 11. Sketch of a compound single-thread channel with low-flow, bankfull, and flood sections

The recommended channel morphology should be considered preliminary; further investigations are needed to refine the channel slope and evaluate sediment sources that could destabilize the proposed design. Ultimately, careful consideration of the meander- or braided-corridor width may benefit the Project and lead to a design that allows for natural sediment transport and bedform development while improving fish passage and minimizing risks to adjacent infrastructure.

Design Discharges Design discharges are needed to size the realigned corridor low-flow, bankfull, and flood sections of the realigned corridor. The hydrologic analyses described in Section 3 were used to inform the selection of design discharges as follows: • Low flow: A low-flow channel should be designed to provide a stream channel to support aquatic

habitat and maintain flow depths and velocities for fish passage during critical periods when discharges may be low. The average daily discharge in Arroyo del Valle was calculated to be 9.4 cfs based on streamflow records from 2002–15 (see Section 3.2.1). This is roughly equivalent to the typical daily discharge in the dry season (May through October). Therefore, it is recommended that the low-flow channel be designed to convey a discharge of around 9 to 10 cfs.

• Bankfull: In alluvial streams, the term “bankfull” refers to the stage or flow at which a stream begins to overtop its banks (i.e., the point of incipient flooding). The bankfull discharge is often used as a surrogate for the channel-forming discharge because it is considered to be the morphologic transition between the active stream channel and the floodplain and the flow that defines channel shape and size in most stable reaches (Leopold et al. 1964). Bankfull or channel-forming flows are generally associated with the 1.5- to 2.3-year recurrence interval (Dunne and Leopold 1978). For preliminary design purposes, it is recommended that the bankfull channel be designed to convey the 2-year peak discharge of 216 cfs, which was calculated based on a regression of post-dam annual peak discharges (see Section 3.2.2).

• Flood: In Alameda County, floodplains are defined and managed according to the area inundated by the 100-year flood event, or the flood that has a 1 percent annual chance of occurrence. According to the Federal Emergency Management Agency’s (FEMA) current Flood Insurance Study (FIS) for Alameda County, the peak 100-year discharge for Arroyo del Valle is 7,000 cfs (FEMA 2011). As noted previously, flood flows in Arroyo del Valle are highly regulated by Del Valle Reservoir. The 100-year flood flow of 7,000 cfs corresponds to a managed flood release from the dam, which differs from the estimated 100-year peak discharge listed in Section 3.2.2 (USACE 1978). The former is regarded as a better estimate because it accounts for the flood storage at Del Valle Reservoir.



Hydraulic Geometry Hydraulic geometry is used to describe the natural stream channel form resulting from the interaction of many environmental factors including climate, land development, sediment sources and transport, bank stability, and riparian assemblage. More simply, the size and shape of a naturally formed stream channel can be related to the frequency and magnitude of the driving forces, particularly discharge.

Field investigations conducted by Balance were an important source of information for determining the preliminary hydraulic geometry for the restored channel (Appendix D). As described in Section 4.3.3, Balance surveyed the channel geometry of Arroyo del Valle at four locations in Sycamore Grove Park and measured the associated channel substrate via pebble counts. The Sycamore Grove Park is unique in that it is less altered by urban encroachments and historical mining operations, which makes it a good reference reach for how the system has responded to the post-dam hydrologic regime. Bankfull flow depths and widths were calculated using the estimated 2-year discharge and standard Manning-Strickler uniform flow equations. The results are shown in Table 5.

Table 5. Bankfull Dimensions Calculated for Cross-Sections in Sycamore Grove Park

Observation point

Morphologic feature

Bankfull dimensions Top Width

(ft) Mean depth

(ft) Cross-sectional

area (ft2) Width-to-depth

ratio

7 Riffle 31 1.6 48 20

8 Riffle 34 1.5 49 23

9 Pool 49 1.2 59 40

10 Pool 44 1.3 56 35

Leopold and Maddock advanced the theory of hydraulic geometry by developing quantitative relationships between the shape of natural channels and discharge using simple power functions (Leopold and Maddock 1953). Dunne and Leopold promulgated the theory by developing several regional curves that relate bankfull channel dimensions (i.e., mean depth, width, and cross-sectional area) to drainage area (Dunne and Leopold 1978).

Building on the work by Dunne and Leopold (1978), Balance has developed its own modified regional curves for bankfull channel dimensions based on data collected in the Bay Area (Hecht, Senter, and Strudley 2013). These curves were used as a secondary method for estimating bankfull dimensions. Rather than using the full watershed area, only the drainage area downstream of the dam was considered because the upper watershed is not expected to significantly contribute to channel-forming discharges. The following dimensions were estimated from the Balance regional curves based on an assumed drainage area of approximately 17 square miles: • Cross-sectional area of 72.1 square feet (ft2) • Channel width of 27.9 feet • Mean channel depth of 2.1 feet

Bankfull relations need to be applied loosely, with due deference for the changes that come with time in an evolving landscape, particularly those heavily affected by anthropogenic modifications. The above-estimated values will be used to help inform the design of the restored channel by providing reasonable target ranges.


4-11


Slope and Sinuosity BC used aerial photography from 2012 to delineate the primary flow path of Arroyo del Valle, starting from Arroyo de la Laguna and ending at the base of Del Valle Dam. Elevations along most of the stream course were obtained from 2006 light detecting and ranging (LiDAR) data provided by Zone 7. Elevations outside of the available LiDAR data were obtained from USGS’s National Elevation Dataset, which is available at a 3-meter resolution that nearly matches the LiDAR data. In addition, historical USGS 7.5-minute quadrangle maps from 1953 were used to approximate the pre-dam profile along Arroyo del Valle for the same reach. The resultant stream profiles, as seen in Figure 12, show three distinct reaches: • Arroyo del Valle below Bernal Avenue has an average slope of approximately 0.35 percent. This

reach flows through Pleasanton and has been substantially altered from its historical condition when the area was covered by the Pleasanton Marsh complex and Arroyo del Valle bifurcated into multiple channels.

• Arroyo del Valle between Bernal Avenue and the Eliot Facility has very little slope as it flows through Boris Lake and Island Pond near the Shadow Cliffs Recreation Area. This reach has also been substantially altered from its historical conditions, largely because of past gravel mining.

• Arroyo del Valle from Island Pond to the base of Del Valle Dam has an average slope of approximately 0.56 percent. This reach has likely degraded from its historical elevation because of gravel mining and the construction of Del Valle Reservoir; however, the 1953 topography does not indicate a substantial decline. The most notable change from 1953 to 2006 appears to be degradation in the vicinity of Lake B and Isabel Avenue, which may suggest continued degradation from past in-channel mining activities.

Figure 12. Arroyo del Valle stream profiles and slope estimates

The stream course delineated from 2012 aerial photography was used to estimate channel sinuosity at incremental lengths along the reach between Island Pond and the mouth of the canyon near Del Valle Dam. The sinuosity of this reach ranges between about 1.05 and 1.15 feet vertical per 1 foot

250

300

350

400

450

500

550

600

0.0 2.0 4.0 6.0 8.0 10.0 12.0

Elev

atio

n (ft

)

Stream Station (miles)

2006 LiDAR and DEM1953 USGS Quads

ISAB

ELAV

ENUE

VALL

ECITO

SRO

AD

SYCAMOREGROVE PARK

LAKE B

LAKE A

SHADOW CLIFFS

ARROYO DE LA LAGUNA

BERN

AL A

VENU

E

DEL VALLE DAM

S ≈ 0.35% S ≈ 0.56%

BORI

SLA

KE

ISLA

ND P

OND



horizontal (ft/ft), with an average sinuosity of 1.14. The estimated sinuosity of the existing channel within Sycamore Grove Park is approximately 1.13. The design sinuosity for the restored channel should be a similar range as those observed on aerial photography; however, the final sinuosity will depend upon the hydraulic characteristics of the channel and stream power required for the anticipated sediment supply.

Alluvial Material Arroyo del Valle and the Eliot Facility overlie the Livermore Formation, which is alluvium consisting of unconsolidated gravel, sand, silt, and clay deposited during the Pliocene, Pleistocene, and Holocene geologic epochs (EMKO 2013). The Livermore Formation is generally divided into three units: Lower Livermore, Upper Livermore, and Quaternary Alluvium. The Eliot Facility is mining Holocene deposits from the Quaternary Alluvium and possibly some Pleistocene deposits from the Upper Livermore Formation. According to KANE GeoTech, Inc. (KANE), a significant amount of the Quaternary Alluvium consists of eroded and transported Upper Livermore sediment, which makes it difficult to differentiate between the two (KANE 2015).

The coarse alluvial fan deposits along Arroyo del Valle are important groundwater recharge areas for the Livermore-Amador Valley (EMKO 2013). Surficial soils at the Project site are classified as Yolo-Pleasanton association (Welch et al. 1966), composed of a mixture of fine-loamy alluvium (Yolo soils) and gravelly fine sandy loam (Pleasanton soils). These are well-drained soils with low to medium runoff potential, and moderately slow to moderate permeability (Welch et al. 1966).

Balance and EMKO performed infiltration testing at the site of the proposed realignment to compare the properties of the native soils with onsite spoil materials and evaluate their suitability as a construction material for the realigned channel and floodplain (Appendix F). The realigned corridor will require cut, fill, and compaction of the spoil soil material present at the site. Thus, existing spoil soil material in the area of the proposed realignment is considered representative of the soil that will compose the substrate under the realigned channel.

Results from field testing indicate that infiltration rates for the spoil material are less (slower) than those observed in native soil materials, indicating that stream channel seepage rates along the restored channel are likely to be less than current rates. Given these results, Balance and EMKO (2016) concluded the following:

[. . .] infiltration of water through the realigned channel of Arroyo del Valle would not steepen the groundwater gradient toward the south edge of Lake B, would not increase the groundwater elevation at the south edge of Lake B, and would not increase the rate of seepage into the south face of Lake B. As such, realignment of Reach-B would not alter the hydrologic conditions along the south side of Lake B in a manner that would be inconsistent with the existing geotechnical slope stability analysis [completed by KANE in 2015].

5-1


Section 5

Conceptual Design As described in Section 1, Option 1 from the Amendment proposes to expand the footprint of Lake B mining (Mitchell Chadwick and Spinardi Associates 2014). To do so, CEMEX proposes to move the arroyo closer to Vineyard Avenue and restore the stream channel and floodplain, creating enhanced riparian and aquatic habitat. A preliminary site layout provided by Spinardi Associates indicates that limiting the total corridor width to 260 feet would allow for 30-foot easements for access roads on either side and still provide adequate space to tie-in to existing grade (Figure 13) (Mitchell Chadwick and Spinardi Associates 2014).

Figure 13. Proposed expansion of Lake B and new alignment

The corridor shown in Figure 13 is approximately 5,800 feet long. The upstream end of the corridor is roughly 390 feet above msl and the downstream end is roughly 360 feet above msl; the resulting slope is approximately equal to the 0.56 percent slope estimated in Section 4.4.3.

Given the site constraints and the findings from the preliminary geomorphic assessment, BC performed hydraulic design calculations to develop channel dimensions and design parameters (Section 5.1). BC then performed a detailed stability analysis based on sediment continuity and the magnitude and frequency of stream flows (Section 5.2). The overall process was iterative because feedback from the stability analysis helped to inform the dimensioning of the channel and floodplain.



Finally, BC formulated a conceptual design (Section 5.3) and prepared concept-level drawings (Appendix A).

5.1 Hydraulic Design Preliminary geomorphic investigations suggest that a single-thread channel with low-flow, bankfull, and flood stages would be appropriate for restoring the arroyo along the new alignment (see Section 4). The following sections describe the development of design parameters for the restored reach (i.e., channel and floodplain) including typical cross-section dimensions, sinuosity and meander patterns, and local variations at bends.

Cross-Section A general, or reach-averaged, cross-section for the compound channel and floodplain was developed based on spatial constraints, geomorphic recommendations, and recognized hydraulic design methodologies. Channel stability analyses (Section 5.2) were performed in parallel to establish a slope and geometry that maintains sediment continuity through the restored reach. The size and configuration of the resultant reach-averaged cross-section are described below: • Low-flow channel: The low-flow channel was designed to convey 9 cfs, which is based on the

average daily discharge and is roughly equivalent to the typical dry season flow releases in Arroyo del Valle. The basic trapezoidal shape has a bottom width of 8 feet and side slopes at 2 (horizontal) to 1 (vertical). An assumed low-flow channel depth of 6 inches provides enough flow capacity, while also providing a bench less than 1 foot above the thalweg that can be used for freshwater marsh and stream habitats. The top width of the low-flow channel is 10 feet.

• Bankfull channel: The bankfull channel will contain the low-flow channel, but will also include a second stage sized to convey the estimated bankfull discharge of 216 cfs. Observations in Sycamore Grove Park indicate that the bankfull channel width for Arroyo del Valle is likely around 31 to 34 feet at riffles and 44 to 49 feet at pools. This is slightly wider than the 28 feet predicted by hydraulic geometry equations for the region, but is considered reasonable; a slightly wider channel is needed to accommodate the compound channel configuration. Assuming a top width of 36.0 feet and 2 to 1 side slopes, the depth of the bankfull channel would need to be 2.1 feet to convey the bankfull discharge, which matches the depth predicted by hydraulic geometry equations for the region.

• Floodplain: The stream corridor will widen considerably above the bankfull depth to provide a floodplain area for dispersing high flows, reducing velocities, and providing space for riparian habitat. Assuming a maximum top width of 260 feet and 3-to-1 side slopes, the floodplain terrace will be approximately 215 feet wide. The floodplain terrace will generally be between 2.1 and 2.5 feet above the thalweg with a gradual slope back toward the bankfull channel. The total depth of the floodplain corridor will depend on the final grading for the Project, but will be around 10 feet above the thalweg. Preliminary hydraulic modeling indicates that there will be more than 3 feet of freeboard between the 100-year water surface (based on the FEMA discharge of 7,000 cfs) and the top of the realigned corridor.

Figure 14 below shows the general cross-section for the realigned corridor with a compound channel and floodplain, including simulated water surface elevations for each of the design discharges. The actual position of the bankfull and low-flow channels will vary laterally across the floodplain because of meandering. Similarly, the depth and width of the bankfull channel will have localized variations when features such as bends, riffles, and pools are added to the design.


5-3


Figure 14. Reach-averaged cross-section widths for compound channel design

Channel Pattern Nearly all natural stream channels have some sinuosity; Leopold and Wolman note that it is unusual for a stream channel to be straight for a distance of more than about 10 channel widths (Leopold and Wolman 1960). In fact, according to Leopold and Langbein (1966) “[scientists] have found that meanders are not mere accidents of nature but the form in which a river does the least work in turning, and hence are the most probable form a river can take.”

For engineering purposes, meanders can be viewed as wave patterns where the distance between two consecutive bends is the wavelength, λ, and the lateral spread between two bends is the amplitude, or the width of the meander belt, Wbelt. Building on their “least work” concept, Langbein and Leopold developed an analytical approach for determining planform meanders based on the theory of minimum variance, which asserts that streams seek the path that provides the minimum variance of bed shear stress and friction, and that this path closely resembles a sine-generated curve (Langbein and Leopold 1966). Figure 15 illustrates how wave parameters can be used to define channel meanders.

Figure 15. Meander and bend parameter definitions

36 ft

10 ft

100-year water surface

Bankfull

Low flow

215 ft

260 ft

3

1

2:1

Bend Apex

Sine-generated curve centerline

Wi

Meander Wavelength (λ)

Wi

Wbelt

Meander belt width

Bankfull channel width=

=Wbelt



Copeland et al. present hydraulic design methodologies for stream restoration projects, including discussions on planform and meander development (Copeland et al. 2001). The equation for a sine-generated meander curve is given as:

𝜙𝜙 = 𝜔𝜔 sin �2𝜋𝜋𝜋𝜋𝜆𝜆𝜆𝜆

�

Where, φ = angle of meander path with the mean longitudinal axis

ω = maximum angle a path makes with the mean longitudinal axis in radians

s = the curvilinear coordinate along the meander path

λ = wavelength

K = sinuosity

Note that λK is often replaced my M, which is the meander arc length.

The angle of the meander path, φ, can be calculated from the curvilinear coordinate along the meander path, s, if all other variables are known. The ordinates of the meander centerline can then be determined by numeric integration, or by approximate methods.

5.1.2.1 Wavelength

Copeland et al. (2001) discusses several relationships for estimating meander wavelength, λ, based on channel width, W, including the following equation developed by Leopold and Wolman (Leopold and Wolman 1960):

𝜆𝜆 = 10.9𝑊𝑊1.01 The formation of meanders in natural streams is driven primarily by stream flow dynamics rather than by sediment or debris loads (Leopold and Wolman 1960; Leopold et al. 1964). Leopold and Wolman describe how meander formation relates to the same flow mechanisms that lead to variation in bed forms, noting that meander wavelength closely resembles riffle and pool spacing (Leopold and Wolman 1960). Hey found that the distance between successive riffles (or pools) equates to roughly 2π times the channel width (2πW), which produces similar results to the wavelength equation presented above (Hey 1976). Thus, using a bankfull width of 36 feet, the design meander wavelength for the restored channel was estimated to be 407 feet using Leopold and Wolman and 452 feet using the Hey relationship (Leopold and Wolman 1960; Hey 1976).

5.1.2.2 Sinuosity

As described in Section 4.4.3, Arroyo del Valle currently exhibits a relatively low sinuosity (K), in the range of 1.05 to 1.15 ft/ft. The existing channel through Sycamore Grove Park—which has shifted to a single-thread form since the construction of Del Valle Dam—has an average sinuosity of approximately 1.13 ft/ft. BC targeted a similar sinuosity for the restored channel by incorporating gradual meanders and bends into the new alignment.

5.1.2.3 Maximum Angle

The maximum angle of the meander path, ω, can be approximated from the sinuosity as given by Mecklenburg and Jayakaran (2012):

𝜔𝜔 = 2√2�1 −1

√𝜆𝜆


5-5


5.1.2.4 Meander Computations

Once wavelength and sinuosity are found, meander calculations can proceed for a series of plotted ordinates. For example, if we assume a wavelength of 407 feet and a sinuosity of 1.13, a meander angle curve can be plotted for a complete wavelength (Figure 16[a]). Then, the ordinates of the meander centerline can then be determined by approximate methods (Figure 16[b]).

Figure 16. Example of a sine-generated meander pattern for λ = 407 and K = 1.13

BC developed a meander pattern for the realigned reach of Arroyo del Valle by applying the sine-generated curve template to a series of meander curves. BC used the uncertainty around the wavelength and sinuosity parameter estimation to introduce more of a naturalistic variation to the planform while still maintaining a stable geometry that is consistent with conditions along existing and upstream reaches. Sinuosity was allowed to vary randomly between 1.0 and 1.2, and wavelength was allowed to vary randomly between 350 and 550 feet. Each sinuosity wavelength parameter set was applied for a distance of four-thirds of the wavelength (4λ/3) before transitioning to the next parameter set. Figure 17 shows the simulated meander pattern for the entire reach.

-1.0

-0.5

0.0

0.5

1.0

0.0 0.2 0.4 0.6 0.8 1.0

Mea

nder

Ang

le, φ

Wave Length

-60-40-20

020406080

100120

0 100 200 300 400Mea

nder

Wid

th (f

t)

Valley Distance (ft)

(b)

sine

cosine



Figure 17. Meander pattern for bankfull channel

The lateral offsets defined by the above meander pattern were applied to the centerline of the realigned corridor (rather than an x-axis) to spatially translate the data and generate real-world geospatial coordinates for the bankfull channel centerline. Left and right bank lines were then generated in ArcGIS4 by creating parallel lines offset by 18 feet (W/2) on either side of the bankfull channel centerline.

Bed and Bend Variation Although the geometry of a stream channel can be described in terms of a reach-averaged cross-section, the actual geometry of the stream will naturally vary along its course. Variations in the width and depth of the channel tend to correlate with bends, as does the formation of pools and riffles. Pools generally form in bends where the channel becomes wider and deeper due to accelerations along the outside of the bend that erode material. Conversely, riffles tend to form areas between bends; channel widths are typically narrower and depths are shallower than those found in pools.

Leopold and Wolman describe how bends generally produce a circular motion that forms helical or spiral flow through meanders, first observed by Thomsen (Leopold and Wolman 1960; Thomsen 1879). Centrifugal force causes superelevation on the outside of a bend, flow is forced downward toward the bed, and increased shear stress on the concave bank causes erosion. As the water moves downstream through the curve it rotates inward toward the convex bank, velocity decreases, and entrained sediment deposits (see Figure 18).

This basic erosional and depositional pattern through the bend creates a deeper pool toward the outside of the bend and a shallower point bar formation on the inside of the bend (Leopold et al. 1964). Riffles form between pools and are generally located near the cross-over, or point of inflection between meander bends (Leopold and Wolman 1960). Riffle sections exhibit shallow, rapid flow with bed sediments that are coarser than those of the pool sections. Figure 19 below illustrates typical bend morphology and shows the general variations in flow depths and cross-section widths.

4 ArcGIS is a desktop GIS application developed by ESRI of Redlands, California: http://www.esri.com/software/arcgis.

-100

-50

0

50

100

0 1000 2000 3000 4000 5000

Late

ral M

eand

er (f

t)

Corridor Distance (ft)

Figure 18. Cross-section showing secondary flow in bends

ErosionDeposition

Helical Flow

Superelevation

http://www.esri.com/software/arcgis


5-7


Figure 19. Typical morphological variations and bed forms within bends

Adapted from Copeland 2001; Harmon et al. 2012 Not drawn to scale

Bank erosion

A

A’

C

C’

B

B’

D Dp

Da

Wi Wp

A A’ B B’

Wa

C C’

Thalweg

Riffle Point bar

Pool

PoolRiffle

PoolRiffle

ThalwegLp

SECTION A-A’ SECTION B-B’

SECTION C-C’

PROFILE

PLAN

PoolRiffle

D

Wa

Da

Dp

Wi

Wp

Lp = pool-pool length= depth at cross-over= depth at pool= depth at bend apex= width at pool

= width at bend apex= width at cross-over



Channel cross-sections within riffles, or the approximate inflection point of the meander, most closely resemble the reach-averaged cross-section described in Section 5.1.1. However, the width and depth of the cross-section tend to increase through the bends as shown in Figure 19.

Copeland presents morphological relationships for width ratios; however, these are applicable to moderate to high sinuosity streams (i.e., sinuosity greater than ~1.2) (Copeland et al. 2001). Alternately, BC used the observed widths in the Sycamore Grove Park reach of Arroyo del Valle to estimate the ratio between the maximum width at the bend apex (pools) and the width at the inflection point (riffles). Top widths presented in Table 5 indicated that bankfull channel widths in bends are approximately 1.43 times greater than bankfull channel widths at riffles. Therefore, for design purposes, the widths will vary from approximately 36 feet in between bends to approximately 52 feet at the apex of bends.

In natural streams, the deepest pool is usually located just downstream of the bend apex. Copeland recommends that restored streams mimic this attribute using a pool-offset ratio, which is the distance from the bend apex to the deepest part of the scour hole divided by the distance from the bend apex to the next downstream inflection point (Copeland et al. 2001). Empirical data presented by Copeland indicate an average pool-offset ratio of 0.36 (Copeland et al. 2001). Thus, the deepest part of the scour hole in a bend should be roughly one-third of the distance between the apex of the bend and the inflection point downstream.

Copeland also provides the following design equation for estimating maximum pool depth based on the mean depth at the inflection point (Copeland et al. 2001):

𝐷𝐷𝑚𝑚𝑚𝑚𝑚𝑚 = 𝐷𝐷𝑚𝑚 �1.5 + 4.5 �𝑅𝑅𝑐𝑐

𝑊𝑊𝑖𝑖�

−1�

Where, Dmax = maximum depth of the scour pool, feet

Dm = mean depth at the inflection point between bends, feet

Rc = radius of curvature of the bend, feet

Wi = width of the channel at the inflection point

The width of the channel at the inflection point is equivalent to the bankfull channel width of 36 feet. The mean depth for the bankfull channel described in Section 5.1.1 is 1.56 feet. The radius of curvature for a sine-generated curve varies; however, a fit can be approximated using an equation presented by Mecklenburg and Jayakaran (Mecklenburg and Jayakaran 2012):

𝑅𝑅𝑐𝑐 =𝜆𝜆𝜆𝜆1.5

13(𝜆𝜆 − 1)0.5

Given the ranges of sinuosity (K) and wavelength (λ) described in Section 5.1.2, the radius of curvature for the bends varies between roughly 100 and 400 feet. Consequently, the maximum depth of the bankfull channel will vary between approximately 2.7 and 4.0 feet in pools just downstream of the designed meander bends.

5.2 Stability Analysis Alluvial channels form and continually shift in response to temporal sequences of flow rate and sediment supply. Over many years, channels adjust to flow and sediment regimes through changes in geometry (e.g., planform, channel dimensions, and longitudinal slope). Given a period with a relatively constant flow regime and sediment supply, a channel approaches a stable geometry and is considered to be in dynamic equilibrium. This is not to say that the channel is static, but rather that morphological responses to extreme events are only temporary and that a more stable morphology is


5-9


continually restored over time by the long-term formative conditions of the system. This geomorphic concept of disturbance, channel adjustment, and dynamic equilibrium is qualitatively represented by Lane’s Principle (Lane 1955):

Qs D50 ∝ Qw S

Where, Qs = sediment load

D50 = the 50th percentile of the sediment grain size distribution

Qw = the stream discharge

S = the channel slope

The relationship represented by Lane’s Principle suggests that a long-term shift in any of these factors would destabilize the system and initiate a compensatory response in one or more of the other factors as the system attempts to restore equilibrium. For example, Lane’s Principle suggests that if sediment supply were to decrease while stream discharges and grain size distribution remained constant, then the channel slope would need to decrease to restore equilibrium. In other words, the stream channel would need to degrade until a new equilibrium slope is reached. This is essentially what happened in 1968 when the construction of Del Valle Dam effectively eliminated the sediment supply from the upper watershed (see Section 4.2.2).

As discussed in Section 4.3.4, signs of degradation and instability can still be observed at some points along Arroyo del Valle, suggesting that the channel may still be adjusting to anthropogenic changes in the watershed. However, given that the dam was constructed more than 45 years ago and that in-channel gravel mining has ceased, it can be assumed that the rate of degradation in the vicinity of Lake B has considerably decreased in recent years. Inspection reports for the SR 84 (Isabel Avenue) bridge corroborate this assumption, stating that the channel under Isabel Avenue degraded 6 feet between 1983 and 1999 but then stabilized.

Given these findings, BC designed the realigned channel to maintain a quasi-equilibrium state by maintaining sediment continuity with upstream reaches. Even so, natural features such as rock weirs and vanes will be incorporated into the design to increase the stability of the bed and banks and reduce the potential for changing conditions or migrating knickpoints to destabilize the system and cause erosion that could threaten adjacent land or infrastructure.

Applying Lane’s Principle at a reach scale, we can evaluate channel stability by comparing the incoming sediment load (supply) with the stream power available to transport that sediment through the reach (capacity). If the sediment supply exceeds the transport capacity, then deposition occurs and the reach is expected to aggrade. Conversely, if the transport capacity exceeds the sediment supply, erosion occurs and the reach is expected to degrade. When the sediment supply and transport capacity are in balance, the reach is expected to maintain a state of dynamic equilibrium. This reach-scale balance of supply and transport is sometimes referred to as sediment continuity.

Calculating Sediment Loads BC calculated long-term sediment loads using a magnitude-frequency analysis, where sediment transport capacities are estimated for a full range of stream discharges and then multiplied by the frequency of occurrence. The magnitude-frequency concept stems from a theory developed by Wolman and Miller describing how the geomorphic evolution of landscapes is strongly influenced by the amount work done by the forces acting on the system—in this case, shear forces caused by flowing water (Wolman and Miller 1960). Figure 20 is a graphical representation of the magnitude-frequency concept where the relative amount of work done depends on both the magnitude of the force and the frequency of occurrence.



Figure 20. Relation between applied stress and frequency of occurrence in geomorphic processes

The frequency of occurrence is log-normally distributed and the magnitude of the influencing force increases in accordance with a power function. The product of the frequency of the occurrences and the magnitude of the influencing

force results in an “effective work” curve (Wolman and Miller 1960).

For an alluvial system, the frequency of flows multiplied by the sediment transport capacity results in a sediment loading curve. The integral of the sediment loading curve is the total sediment load. If the frequency of occurrence is based on a finite period of time, such as a year, then the calculated sediment load represents the periodic average, or in the case of a year, the average annual transported sediment load.

Flow Frequency Curve. BC analyzed long-term measured streamflow data for Arroyo del Valle during both pre-dam and post-dam conditions (see Section 3.2.1). The historical flow frequency histogram developed for the post-dam condition is assumed to represent a reasonable approximation of existing and future flow regime. As such, the histogram data shown in Figure 5 can effectively be used approximate the flow frequency curve (curve b in Figure 20).

Sediment Transport Curve. BC reviewed the sediment transport analysis documented in the Zone 7 Stream Management Master Plan and found that Ayres Associates developed the bedload transport function based on a regression analysis, the Meyer-Peter and Muller bedload equation, and the Zeller and Fullerton Power Function (RMC 2006; Ayres Associates 2001). The Ayers Associates transport function is shown below (Ayers Associates 2001):

𝑞𝑞𝑠𝑠 = 0.000157𝐺𝐺𝐺𝐺0.45𝑉𝑉3.65

𝐷𝐷500.61𝐷𝐷0.29

where: qs = unit width total load transport capacity (cfs/ft)

Gr = gradation coefficient of the bed material = 12

�𝐷𝐷84𝐷𝐷50

+ 𝐷𝐷50𝐷𝐷16

�

V = average flow velocity (feet per second [ft/s])

Applied Stress (Flow Rate)

a.Ra

te of

sedim

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D50 = material size of which 50 percent of the sediment by weight is smaller (millimeters [mm])

D = hydraulic depth (ft)

BC calculated sediment transport capacity in Arroyo del Valle using the above equation. Bed sediment material sizes were estimated based on data collected by Balance (Appendix E). Flow depths and velocities were calculated using standard uniform flow calculations; channel slopes and cross-sectional geometries were based on the 2006 LiDAR data provided by Zone 7. Appendix G provides additional information on the magnitude-frequency approach, as well as the computational methods and assumptions used to calculate sediment loads.

Balancing Sediment Loads BC evaluated average annual sediment loads for four reaches of Arroyo del Valle as shown in Figure 21 and described below: • Shadow Cliffs Reach: downstream of the proposed realignment where Arroyo del Valle flows

through Island Pond and Boris Lake • Lake B Reach: adjacent to Lake B from just upstream of Island Pond to Isabelle Avenue • Lake A Reach: adjacent to Lake A from Isabelle Avenue to Vallecitos Road • Sycamore Grove Park Reach: upstream of Vallecitos Road through Sycamore Grove Park

Figure 21. Reaches of Arroyo del Valle used for sediment continuity analysis



BC began by calculating average annual sediment loads for each of the four reaches under existing conditions and found that the reaches along Lake B, Lake A, and Sycamore Grove Park transport roughly equivalent sediment loads—in the range of 100,000 to 120,000 tons per year—while the Shadow Cliffs Reach transports considerably less at around 5,000 tons per year (Figure 22). This latter difference was expected, because Island Pond and Boris Lake appear to trap sediments. The low-energy gradient created by the impounded water reduces stream power and tends to create highly depositional conditions.

BC performed the hydraulic design evaluations described in Section 5.1 in parallel with the sediment continuity calculations so the average annual sediment load for the new realigned reach could be compared with the sediment loads transported from upstream reaches under existing conditions. Hydraulic design parameters such as cross-sectional dimensions and channel sinuosity/slope were adjusted to nearly match the sediment loads, thus creating a realigned stream channel that balances or maintains sediment continuity with upstream reaches (Figure 22).

Figure 22. Average annual sediment load transported through Arroyo del Valle reaches

Reaches defined in Figure 21; SGP = Sycamore Grove Park.

In addition to comparing the total sediment load estimates, BC examined the sediment loading curve and the distribution of the sediment load, i.e., the discharge ranges predicted to transport the most sediment. Cumulative sediment loadings were plotted for the realigned reach and the two upstream reaches, Lake A and Sycamore Grove Park (Figure 23, below). The cumulative distribution of sediment loads shown in Figure 23 exhibit similar patterns, which suggests that the realigned channel will transport comparable sediment loads over similar discharge ranges.

0

20

40

60

80

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120

Shadow Cliffs Lake B Lake A SGP

Sedi

men

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Existing

Realigned


5-13


Figure 23. Cumulative sediment loading curves

The reader should note that sediment continuity analyses, such as those presented in this section, are inherently uncertain and require careful consideration of the assumptions and limitations of the available data. Two important limitations include: • Extreme events are not included in the historical record: The post-dam streamflow data used for

this analysis do not include extreme events such as the 100-year flood. The infrequency of these types of events reduces their long-term significance; however, it is quite possible that a large flood event would cause a substantial—even if only temporary—disturbance to the geomorphic balance of the stream system.

• Sediment yield to Arroyo del Valle downstream of the Del Valle Dam is unknown: As mentioned previously, Del Valle Dam traps most of the sediment load that used to come from the upper reaches of Arroyo del Valle. In fact, using a relation developed by Brune, BC estimated that 97 percent of the sediment flowing into Del Valle Reservoir is trapped behind the dam (Brune 1953). BC performed some preliminary calculations to estimate sediment yields to the Arroyo del Valle reaches downstream of the Del Valle Dam and found that inflowing sediment yields could be less than half of the sediment loads calculated for the Lake B, Lake A, and Sycamore Grove Park reaches. This suggests that sediment loads originating from Sycamore Grove Park could be largely due to the reworking of alluvial material immediately downstream of the Del Valle Dam and in Sycamore Grove Park. Therefore, even though there is some evidence that Arroyo del Valle has stabilized, there may still be potential for degradation and reduced sediment loads in those upstream reaches.



5.3 Formulating the Design Concept The hydraulic design parameters developed in Section 5.1 were applied to the site to form a complete design concept. Figure 24 provides an overview of the proposed realigned channel. Appendix A provides a concept-level drawing set with a plan and profile of the proposed alignment.

Figure 24. Conceptual design overview

The realigned channel begins about 1,600 feet downstream of Isabel Avenue at an elevation of roughly 393 feet above msl. The new alignment briefly parallels the existing channel and then shifts southwest closer to Vineyard Avenue. Construction of the new channel and floodplain corridor will eliminate an existing remnant lake at the southern edge of the site and restore an uninterrupted stream channel. The downstream end of the realigned channel will tie back into the existing channel several hundred feet northwest of the future extent of Lake B at an elevation of roughly 358 feet above msl. The realigned corridor extends roughly 5,800 linear feet and the realigned bankfull channel within the floodplain extends approximately 6,200 linear feet.

Tributaries Topographic mapping, aerial photos, and onsite observations indicate that at least two, and possibly three, significant tributaries flow into Arroyo del Valle between the proposed upstream and downstream tie-in points. The drainage areas for these tributaries range between about 0.5 to 2 square miles. It is recommended that these be incorporated into the design to create controlled and stable confluences with the proposed new channel.


5-15


Transitions Transitions at the upstream and downstream points will need to be designed to reduce the potential for an avulsion that could allow the stream to abandon the new alignment. The banks of the new bankfull channel and the side slope of the floodplain should be reinforced and stabilized using natural features such as those described in the California Salmonid Stream Habitat Restoration Manual (Flosi et al. 2010). These could include live vegetated crib walls, native material revetments, log wing-deflectors, and tree revetments. The banks of the new channel should be extended and tied into the outer slopes of the existing floodplain to intercept flow from a wider area and minimize the potential for Arroyo del Valle to shift channels upstream and flank the transition point. This concept is illustrated in Figure 25.

Figure 25. Schematic of bank tie-in at upstream transition

The transition at the downstream end of the realignment can be allowed to flow more freely. The channel banks and floodplain side slopes can simply be graded to provide a smooth and gradual transition back into the existing geometry.

Existing floodplain

Proposed thalwegRelic channel/flowpathExisting low-flow channel

Proposed stabilized banks

L E G E N D



Additional Features Given the considerable uncertainty associated with transient and highly variable phenomena such as sediment loads, transport rates, and equilibrium dynamics, BC recommends that additional features be added to the design to help mitigate disturbances that could lead to severe degradation or channel widening. Such design provisions might be avoided if the realigned corridor was extremely wide and unconfined, where unexpected or extreme shifts in the channel might go unnoticed. However, the Project site is located in a developed area, bounded by Vineyard Avenue to the south and Lake B to the north, as well as utilities and other infrastructure in the vicinity. Therefore, as the design progresses, natural features that offer increased stability should be added, particularly to vulnerable areas such as the outsides of bends. These types of features offer a dual purpose by both promoting a stable channel configuration and providing a more reliable platform for ecological restoration as plant communities are established and fish-passable features are created. As cited previously, documents such as the California Salmonid Stream Habitat Restoration Manual (Flosi et al. 2010) provide a variety of alternatives for habitat improvements, fish passage, and bank stabilization techniques.

6-1


Section 6

Conclusions and Recommendations Under Option 1 of the Amendment, CEMEX proposes to move Arroyo del Valle south along a new alignment parallel to Vineyard Avenue to allow for expansion of Lake B. At the same time, CEMEX will restore and enhance the Arroyo del Valle corridor to create a complex and varied aquatic habitat for vertebrates and native plant species. Regulatory agencies such as the RWQCB have requested an assessment of the geomorphic conditions of Arroyo del Valle and additional design evaluations to confirm that the realigned channel will be stable and persist, while still providing the natural form and function needed to support fish and native habitats. BC has prepared this Concept Design Report to respond to those inquiries and to provide preliminary design drawings and information for use during subsequent design stages.

The preliminary geomorphic assessment of Arroyo del Valle found a highly modified fluvial system that has been altered and channelized, and the hydrologic and sediment regimes dramatically changed by the construction of Del Valle Reservoir. It is likely that the stream is still adjusting to these impacts and continued land use changes. While the stream degradation caused by the dam has likely diminished, there is still the risk of instability and continued channel evolution. In addition, channels adjust naturally to episodic events such as watershed-scale wildfires and floods.

Given this dynamic setting, there is no single absolute size and configuration for a restored reach of Arroyo del Valle. Channel restoration design efforts for Arroyo del Valle should focus on establishing a suitable range of channel geometries that will allow for some adjustment over time to accommodate the flow and sediment regime it will experience.

Section 5 describes the development of single-thread compound channel with low-flow, bankfull, and flood stages. Given the site constraints and the findings from the preliminary geomorphic assessment, BC performed hydraulic design calculations and a sediment continuity-based stability analysis to develop design parameters such as channel widths, depths, slope, and sinuosity. To a large extent, these analyses were informed by the conditions observed upstream in Sycamore Grove Park.

Given the considerable uncertainty associated with sediment loads, transport estimates, and equilibrium dynamics, BC recommends that additional features be added to the design to help mitigate disturbances that could lead to severe degradation or channel widening. These features and similar improvements should be investigated as the design progresses. The following bullets summarize BC’s recommendations for further study: • Coordinate with Alameda County and other relevant permitting agencies to apprise them of the

latest design concept and begin to elicit feedback on the conceptual design. Relevant permitting agencies could include California Fish and Game (California Code Sections 1601/1603- Streambed Alteration Agreement), USACE (Section 404 of the Clean Water Act), California RWQCB (Section 401 of the Clean Water Act), and National Marine Fisheries Service (NMFS) for potential impacts to federally listed species.



• The Alameda Creek watershed is listed as one of the eight anchor watersheds in the San Francisco Estuary that support the federally listed threatened Central California Coast steelhead trout (CCCST). While there are currently barriers to fish passage downstream of the Project site, fish passage may become a key objective for the Project. Additional studies will need to be conducted and the design will need to be refined to accommodate specific fish habitat and passage criteria.

• Arroyo del Valle is a highly disturbed system. Findings from the initial geomorphic assessment support the design concept; however, this is not a static system and conditions continue to change over time. Additional investigations are in process to inform the final design.

• Continue to advance the Project through design development, construction documents, and permitting. The process to advance the design of this Project will be determined by CEMEX’s preferred method for construction and the requirements of the necessary permits. For example, CEMEX may develop a complete bid package that includes detailed plans and specifications for the entire Project. However, CEMEX can employ an alternative delivery method in which the design documents are less detailed, and the Project engineer is very engaged during construction of the Project. In both instances, the design documentation would be used to secure permits and in a competitive bid process to secure a construction contractor.

7-1


Section 7

Limitations This document was prepared solely for CEMEX in accordance with professional standards at the time the services were performed and in accordance with the contract between CEMEX and Brown and Caldwell dated November 18, 2015. This document is governed by the specific scope of work authorized by CEMEX; it is not intended to be relied upon by any other party except for regulatory authorities contemplated by the scope of work. We have relied on information or instructions provided by CEMEX and other parties and, unless otherwise expressly indicated, have made no independent investigation as to the validity, completeness, or accuracy of such information.

This document sets forth the results of certain services performed by Brown and Caldwell with respect to the property or facilities described therein (the Property). CEMEX recognizes and acknowledges that these services were designed and performed within various limitations, including budget and time constraints. These services were not designed or intended to determine the existence and nature of all possible environmental risks (which term shall include the presence or suspected or potential presence of any hazardous waste or hazardous substance, as defined under any applicable law or regulation, or any other actual or potential environmental problems or liabilities) affecting the Property. The nature of environmental risks is such that no amount of additional inspection and testing could determine as a matter of certainty that all environmental risks affecting the Property had been identified. Accordingly, THIS DOCUMENT DOES NOT PURPORT TO DESCRIBE ALL ENVIRONMENTAL RISKS AFFECTING THE PROPERTY, NOR WILL ANY ADDITIONAL TESTING OR INSPECTION RECOMMENDED OR OTHERWISE REFERRED TO IN THIS DOCUMENT NECESSARILY IDENTIFY ALL ENVIRONMENTAL RISKS AFFECTING THE PROPERTY.

Further, Brown and Caldwell makes no warranties, express or implied, with respect to this document, except for those, if any, contained in the agreement pursuant to which the document was prepared.

All data, drawings, documents, or information contained in this report have been prepared exclusively for the person or entity to whom it was addressed and may not be relied upon by any other person or entity without the prior written consent of Brown and Caldwell unless otherwise provided by the Agreement pursuant to which these services were provided.

Limitations Conceptual Design for Arroyo del Valle Realignment at Lake B



8-1


Section 8

References Allardt GF. 1874. “Official map of Alameda County, California.” Courtesy of The Bancroft Library, UC Berkeley.

Ayres Associates. 2001. Zone 7 Water Agency Geomorphic and Sediment Transport Evaluation. Prepared for Zone 7 Water Agency and West Yost and Associates. December.

Balance Hydrologics, Inc. (Balance) 2016. Technical Memorandum: Initial Geomorphic Assessment and Conceptual Design for Reach B, Arroyo del Valle on the CEMEX Eliot Facility, Alameda County, California. July 14, 2016. [document included in Appendix D]

Bledsoe, B.P. and C.C. Watson. April 2001. “Effects of Urbanization on Channel Stability.” Journal of the American Water Resources Association; Vol. 37, No. 2, p. 255–270.

Boardman WF. 1870. “Plat of survey: Rancho El Valle de San Jose.” Courtesy of Museum of Local History, Fremont, California.

Booth, D. B. 1990. “Stream-channel incision following drainage-basin urbanization.” Water Resources Bulletin; v. 26, p. 407–417.

Brune, G.M. 1953. “The trapping efficiency of reservoirs.” Transactions of the American Geophysical Union. Number 34: 407–418.

Collins, B. and T. Dunne. 1990. Fluvial Geomorphology and River-Gravel Mining: A Guide for Planners, Case Studies Included. California Department of Conservation Division of Mines and Geology, Special Publication 98.

Copeland, Ronald R., McComas, Dinah N., Thorne, Colin R., Soar, Philip J., Jonas, Meg M. 2001. Hydraulic Design of Stream Restoration Projects. Engineer Research and Development Center Coastal and Hydraulics Lab; Vicksburg, Mississippi.

Duerr. 1872. “Survey No. 1528.” Courtesy of Alameda County Department of Public Works.

Dunne, Thomas and Leopold, Luna B. 1978. Water in Environmental Planning. San Francisco: W. H. Freeman and Company.

Federal Emergency Management Agency (FEMA). 2009. Flood Insurance Study for Alameda County, California and Incorporated Areas. Effective August 3, 2009. Flood Insurance Study Number 06001CV001A.

Flosi Gary, Scott Downie, James Hopelain, Michael Bird, Robert Coey, and Barry Collins. 2010. California Salmonid Stream Habitat Restoration Manual, Fourth Edition. State of California, The Resources Agency, California Department of Fish and Game, Wildlife and Fisheries Division.

Gibbes C.D. 1878. Subdivisions of Plot 31 Rancho El Valle de San Jose. 1 inch=10 chains. Courtesy of Alameda County Department of Public Works.

EMKO. 2013. Updated Hydrology and Water Quality Analysis Report for Lake A, Lake B, and Lake J, CEMEX Eliot Quarry – SMP-23, Pleasanton, California. June 7. Prepared by: EMKO Environmental, Inc. 551 Lakecrest Drive, El Dorado Hills, California 95762.

Harman, W., R. Starr. 2011. Natural Channel Design Review Checklist. U.S. Fish and Wildlife Service, Chesapeake Bay Field Office, Annapolis, Maryland.

Harman, W., R. Starr, M. Carter, K. Tweedy, M. Clemmons, K. Suggs, C. Miller. 2012. A Function-Based Framework for Stream Assessment and Restoration Projects. US Environmental Protection Agency, Office of Wetlands, Oceans, and Watersheds, Washington, DC EPA 843-K-12-006.

References Conceptual Design for Arroyo del Valle Realignment at Lake B


Hecht, B., Senter, A., Strudley, M. 2013. New bankfull geometry relations for Inland South Bay and Monterey Bay, Central California. Poster presented at the State of the Estuary Biannual Conference, Oakland, California. October.

Helley, E.J., and Graymer, R.W. 1997. Quaternary geology of Alameda County, and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin Counties, California: A digital database. U.S. Geological Survey Open-File Report 97–97.

Hey, R.D. 1976. “Geometry of river meanders.” Nature 262:482–484.

Interagency Advisory Committee on Water Data (IACWD). 1982. Guidelines for Determining Flood Flow Frequency, Bulletin 17B of the Hydrology Subcommittee. United States Department of the Interior, USGS, Office of Water Data Coordination; Reston, Virginia.

Kamman Hydrology & Environmental Engineering, Inc. (Kamman). 2009. Phase 2 Technical Report, Sycamore Grove Recovery Program, Sycamore Grove Park, Livermore, California. Prepared for Livermore Area Recreation and Park District 4444 East Avenue, Livermore, California 94550 and the Zone 7 Water Agency 100 North Canyons Parkway, Livermore, California 94551. Edited by Kamman Hydrology & Engineering, Inc., 7 Mt. Lassen Drive, Suite B250, San Rafael, California 94903.

KANE GeoTech, Inc. (KANE). 2015. CEMEX Eliot Quarry Geotechnical Characterization Report Alameda County, California. Prepared by KANE Geotech, Inc., 7400 Shoreline Drive, Ste. 6 Stockton, California 95219.

Kondolf, G.M and Matthews, W.V. 1991. Management of coarse sediment in regulated rivers of California. University of California Water Resources Center Technical Report 748.

Langbein, W.B. and L.B. Leopold. 1966. River Meanders Theory of Minimum Variance. Geological Survey Professional Paper 422-H United States Government Printing Office, Washington.

Leopold, L.B. 1968. Hydrology for Urban Land Planning—A Guidebook on the Hydrologic Effects of Urban Land Use. Geological Survey Circular 554.

Leopold, L.B. and W.B. Langbein. 1966. “River Meanders.” Scientific American. June, pp. 60–69.

Leopold L.B. and M.G. Wolman. 1960. “River Meanders.” Bulletin of the Geological Society of America. Vol. 71. pp. 769–794.

Leopold, L.B., M.G. Wolman, and J.P. Miller, 1964. Fluvial Processes in Geomorphology. Freeman, San Francisco, California. ISBN 0-486-68588-8.

Leopold, L. B. and Maddock, T. J. 1953. Hydraulic geometry of stream channels and some physiographic implications. U. S. Geological Survey Professional Paper 252, 55 p.

LSA Associates (LSA). 2013. “Results of Biological Surveys, CEMEX Eliot Quarry, Alameda County, California.” Letter to Ron Wilson, CEMEX, 5180 Golden Foothills Parkway, El Dorado Hills, California 95762 from Malcolm J. Sproul, LSA Associates, Inc., 157 Park Place Point, Richmond, California, 94801.

Mecklenburg, D.E. and A.D. Jayakaran. 2012. “Dimensioning the Sine-Generated Curve Meander Geometry.” Journal of the American Water Resources Association. 1-8. DOI: 10.1111 ⁄ j.1752-1688.

Meehan, W.R. and W.S. Platts. 1978. Livestock Grazing and the Aquatic Environment. Journal of Soil and Water Conservation, Volume 33, Number 6.

Mitchell Chadwick and Spinardi Associates. 2014. Reclamation Plan Amendment, CEMEX SMP-23, 1544 Stanley Boulevard, Pleasanton, California 94566, Unincorporated Alameda County, Submitted to: Alameda County Community Development Agency Neighborhood Preservation and Sustainability Department, 224 W. Winton Ave, Suite 205, Hayward, California 94544, Prepared by: Spinardi Associates, 265 Sea View Avenue, Piedmont, California 94610. June.

Raines, Melton & Carella, Inc. (RMC). 2006. Zone 7 Stream Management Master Plan. Appendix C.

San Francisco Estuary Institute (SFEI). 2013. Alameda Creek Watershed Historical Ecology Study. February.

Schumm, A., Watson, C., and Harvey, M. 1984. Incised Channels: Morphology, Dynamics and Controls, Water Resources Publications, Littleton, Colorado.

Conceptual Design for Arroyo del Valle Realignment at Lake B References

8-3


Simon, A., Hupp, C.R. 1986. Channel evolution in modified Tennessee channels. Proceedings, Fourth Federal Interagency Sedimentation Conference, Las Vegas, March 24–27, 1986, vol. 2, pp. 5–71–5–82.

Simon, A., and M. Rinaldi. 2006. Disturbance, Stream incision, and Channel Evolution: The Roles of Excess Transport Capacity and Boundary Materials in Controlling Channel Response. Geomorphology, 79: 361-383.

Taylor, Ross N. and Michael Love. 2010. California Salmonid Stream Habitat Restoration Manual, Volume 2, 4th edition; Part IX Fish Passage Evaluation at Stream Crossings. Added to the manual in April 2003.

Thompson, West. 1878. “Official and historical atlas map of Alameda County,” California Oakland, CA: Thompson & West.

Thomsen, J. 1879. “On the origin of windings of rivers in alluvial plains”: Royal Soc. London Proc., v. 25, p. 5-6

U. S. Geological Survey (USGS). 1906. “Livermore Quadrangle, California”: 15-minute series (Topographic) 1:62,500.

Welch, L.E., Huff, R.C., Dierking, R.A., Cook, T.D., Bates, L.A., and Andrews, W.F. 1966. Soil survey of the Alameda area, California. United States Department of Agriculture, Soil Conservation Service, in cooperation with the California Agricultural Experiment Station.

Westover HL, van Duyne C. U.S. Department of Agriculture, Bureau of Soils. 1910. Livermore Soil Map. 1:625,000.

Williams, G.P. and Wolman, M.G. 1984. Downstream effects of dams on alluvial rivers. U.S. Geological Survey Professional Paper 1286

Wines, Brian. 2015. Water Resource Control Engineer, San Francisco Bay Regional Water Quality Control Board, Letter to James Gilford Alameda County Neighborhood Preservation and Sustainability, August 7, 2015 CIWQS Place ID No. 237327. Subject: Notice of Preparation for the Eliot Facility (SMP-23) Reclamation Plan, Amendment, Draft Environmental Impact Report. SCH No. 2015072020

Wolman, M.G., and J.P. Miller. 1960. “Magnitude and Frequency of Forces in Geomorphic Processes.” Journal of Geology; v. 68, p. 54–74.

WRECO. 2009. Bridge Design Hydraulic Study Report 04-ALA-84 State Route 84 Expressway Widening Project EA 297601 Cities of Livermore and Pleasanton, Alameda County, California 33C0710/33C0713. May.

References Conceptual Design for Arroyo del Valle Realignment at Lake B



A-1


Appendix A: Conceptual Design Drawings

Appendix A Conceptual Design for Arroyo del Valle Realignment at Lake B

A-2 CEMEX AdVR Concept Design 20160718.docx


CONCEPT DESIGNARROYO DEL VALLE REALIGNMENT AT LAKE B

DRAWING INDEX1 FIGURE T-1 TITLE SHEET

2 FIGURE C-1 OVERALL SITE PLAN

3 FIGURE C-2 PLAN AND PROFILE -STA 0+00 TO STA 25+00

4 FIGURE C-3 PLAN AND PROFILE -STA 25+00 TO STA 50+00

5 FIGURE C-4 PLAN AND PROFILE -STA 50+00 TO STA 65+21±

6 FIGURE C-5 STREAM SECTIONVICINITY MAPSCALE: NONE

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B-1


Appendix B: Additional Flow Data

Appendix B Conceptual Design for Arroyo del Valle Realignment at Lake B

B-2 CEMEX AdVR Concept Design 20160718.docx


Conceptual Design for Arroyo del Valle Realignment at Lake B Appendix B

B-3


Figure B-1. Monthly discharges for Arroyo del Valle based on pre-dam average daily discharges

Figure B-2. Monthly discharges for Arroyo del Valle based on post-dam average daily discharges

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Appendix B Conceptual Design for Arroyo del Valle Realignment at Lake B

B-4 CEMEX AdVR Concept Design 20160718.docx

Figure B-3. Peak discharge frequency for Arroyo del Valle based on peak annual discharge data from AVL

Figure B-4. Peak discharge frequency for Arroyo del Valle based on peak annual discharge data from AVL

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C-1


Appendix C: Bulletin 17B Approach

Appendix C Conceptual Design for Arroyo del Valle Realignment at Lake B

C-2 CEMEX AdVR Concept Design 20160718.docx


Conceptual Design for Arroyo del Valle Realignment at Lake B Appendix C

C-3


Frequency Analysis Using Bulletin 17B Approach (IACWD 1982) Statistical parameters such as mean values, standard deviations, and skewness are used to fit the peak discharge data to a log-Pearson Type III (LP3) distribution that can be used to estimate the likelihood of various discharges as a function of recurrence interval, or exceedance probability. The advantage of this technique is that extrapolation can be used to estimate values for events with return periods beyond the period of record. The LP3 distribution is calculated using the following general equation:

log 𝑥𝑥 = log 𝑥𝑥�� + 𝜆𝜆𝜎𝜎log 𝑚𝑚 Equation 6

where x is the discharge value of some specified probability, log 𝑥𝑥�� is the average of the log x discharge values, K is a frequency factor, and 𝜎𝜎log 𝑚𝑚 is the standard deviation of the log x values. The frequency factor K is a function of the skewness coefficient and recurrence interval and can be approximated using the following formula (Kite 1977; Chow et al. 1988):

𝜆𝜆 = 𝑧𝑧 + (𝑧𝑧2 − 1)𝑘𝑘 +13

(𝑧𝑧3 − 6𝑧𝑧)𝑘𝑘2 − (𝑧𝑧2 − 1)𝑘𝑘3 + 𝑧𝑧𝑘𝑘4 +13

𝑘𝑘5 Equation 7

where z is the standard normal variable and k is equal to the coefficient of skewness (Cs) divided by 6. The coefficient of skewness is calculated as follows:

𝐶𝐶𝑠𝑠 =𝑛𝑛 ∑�log 𝑥𝑥 − log 𝑥𝑥��3

(𝑛𝑛 − 1)(𝑛𝑛 − 2)�𝜎𝜎log 𝑚𝑚�3

Equation 8

where n is the number of values in the data set. The skewness estimate (Cs) computed using Equation 6 is referred to as the station skew because it is based solely on data from the station of interest. Error and bias in the skewness estimate increase as the number of data values (n) decrease. Bulletin 17B recommends the use of a weighted coefficient of skewness (Cw) that not only accounts for the station skew, but also incorporates a generalized estimate of the coefficient of skewness (Cm) developed from data observed at other sites within the region:

𝐶𝐶𝑤𝑤 =𝑉𝑉(𝐶𝐶𝑚𝑚)𝐶𝐶𝑠𝑠 + 𝑉𝑉(𝐶𝐶𝑠𝑠)𝐶𝐶𝑚𝑚

𝑉𝑉(𝐶𝐶𝑚𝑚) + 𝑉𝑉(𝐶𝐶𝑠𝑠)

Equation 9

where V(Cm) is the variance of the generalized skew and V(Cs) is variance of the station skew. BC estimated the generalized skew (Cm) to be -0.6 and the variance of the generalized skew, V(Cm), was assumed to be 0.14 based the regional study for California prepared by Parrett (Parrett et al. 2011).

The variance of the station skew, V(Cs), for LP3 random variables can be obtained from the results of Monte Carlo experiments by Wallis, which showed that (Wallis et al. 1974):

𝑉𝑉(𝐶𝐶𝑠𝑠) = 10𝐴𝐴−𝐵𝐵 log�𝑛𝑛10� �

Equation 10

where A = -0.33 + 0.08 |Cs| if |Cs| ≤ 0.90 or A = -0.52 + 0.30 |Cs| if |Cs| > 0.90; and B = 0.94 - 0.26 |Cs| if |Cs| ≤ 1.50 or B = 0.55 if |Cs| > 1.50. Note that |Cs| is the absolute value of the station skew.

Appendix C Conceptual Design for Arroyo del Valle Realignment at Lake B

C-4 CEMEX AdVR Concept Design 20160718.docx

Appendix C References Chow, V.T., D.R. Maidment and L.W. Mays. 1988. Applied Hydrology. New York u.a., McGraw-Hill, pp. 392.

Interagency Advisory Committee on Water Data (IACWD). 1982. Guidelines for Determining Flood Flow Frequency, Bulletin 17B of the Hydrology Subcommittee. United States Department of the Interior, USGS, Office of Water Data Coordination; Reston, Virginia.

Kite, G.W. 1977. Frequency and Risk Analysis in Hydrology. Water Resources Publications. Fort Collins, Colorado.

Parrett, Charles, Andrea Veilleux, J.R. Stedinger, N. A. Barth, Donna L. Knifong, and J.C. Ferris. 2011. Regional Skew for California, and Flood Frequency for Selected Sites in the Sacramento-San Joaquin River Basin Based on Data through Water Year 2006. Prepared in cooperation with the Federal Emergency Management Agency, the U.S. Army Corps of Engineers, and the U.S. Forest Service. Scientific Investigations Report 2010-5260, U.S. Geological Survey, Reston, Virginia: 2011

Wallis, J.R., N.C. Matalas, J.R. Slack. 1974. Just a Moment. Water Resources Research, Vol. 10, No. 2, pp. 211–219.

D-1


Appendix D: Initial Geomorphic Assessment

The following document is a draft version used to support development of the conceptual design. Geomorphic investigations are continuing and will be updated as the project continues. Where information in this appendix conflicts with information contained in the main document, refer the main document.

Appendix D Conceptual Design for Arroyo del Valle Realignment at Lake B

D-2 CEMEX AdVR Concept Design 20160718.docx


Integrated Surface and Ground Water Hydrology • Wetland and Channel Restoration • Water Quality • Erosion and Sedimentation • Storm Water and Floodplain Management

800 Bancroft Way • Suite 101 • Berkeley, CA 94710 • (510) 704-1000

224 Walnut Avenue • Suite E • Santa Cruz, CA 95060 • (831) 457-9900 PO Box 1077 • Truckee, CA 96160 • (530) 550-9776

www.balancehydro.com • email: [email protected]

July 14, 2016 Nathan Foged, P.E. Project Manager Brown and Caldwell 701 Pike Street, Suite 1200 Seattle, Washington 98101 RE: Technical Memorandum: Initial Geomorphic Assessment and Conceptual Design for Reach

B, Arroyo del Valle on the CEMEX Eliot Facility, Alameda County, California

This technical memo describes our initial geomorphic and hydrologic assessment of Reach B on Arroyo del Valle on the CEMEX Construction Materials, Inc., (CEMEX) Eliot facility, Pleasanton, California. The memo is limited to recommendations for the configuration of a low-flow channel designed to convey 10 cfs, the average daily flow for Arroyo del Valle during non-runoff periods. Results from this assessment may provide an initial basis for the development of a restoration design for Reach-B on Arroyo del Valle.

It is our understanding that the channel restoration on Reach-B of Arroyo del Valle is one part of the Reclamation Plan Amendment for the CEMEX Eliot Facility, Surface Mining Permit –23 (SMP-23) located in Alameda County. CEMEX is seeking to amend SMP-23 to:

Eliminate the need for drop structures and enable the Arroyo del Valle to flow uninterrupted along the south boundary of Lakes A and B (two previously approved drop structures would be removed from the plan so that Arroyo del Valle can be re-routed around, instead of through, Lakes A and B).

Reconfigure Lake B to provide a wildlife corridor that includes the re-routed Arroyo del Valle.

Adjust the depth of Lake B to 150 feet above mean sea level (MSL).

This technical memo provides some of the underpinnings to guide these amendments in a manner which adds to resource values. The memo presents a conceptual approach, particularly for item 1, above; it is not intended as a blueprint or basis for design until further work is conducted.

Project Background

CEMEX seeks to restore and reclaim Reach-B on Arroyo del Valle on its Eliot Facility in Pleasanton, California. The Regional Water Quality Control Board (RWCQB), California Department of Fish and Wildlife (CDFW), and the Army Corps of Engineers (USACE) have raised concerns about the channel

Balance Hydrologics, Inc. Nathan Foged, P.E. July 14, 2016 Page 2

215101 Design Recommendation Letter 07-14-2016_FNL

restoration as incorporated in the Reclamation Plan presently in effect for Reach-B, particularly regarding channel stability and passage habitat for steelhead trout (Oncorhynchus mykiss).

Alameda Creek is listed as one of the eight anchor watersheds in the San Francisco Estuary that support the Federally Threatened Central California Coast steelhead trout (CCCST). A major habitat-management goal for Arroyo del Valle is to improve fish passage and habitat downstream of the 222-foot Del Valle Dam. Comments from the Regional Water Quality Control Board staff have clarified that enabling fish passage for CCCST will be one of their primary goals for Reach-B, with spawning and rearing habitat to occur upstream of the project site.

Major natural-resource plans for the area include: the Basin Plan of the Regional Water Quality Control Board, the various plans for protection and recovery of the Alameda Creek CCCST run, the Specific Plan for the Chain of Lakes, Zone 7 Water Agency, and efforts to protect the natural, native woody riparian vegetation corridor along the creek. The reclamation plan for Reach-B on Arroyo del Valle should incorporate elements that fit within this set of prior public plans, as well as CEMEX’s Reclamation Plan. The overriding focus for management of riparian vegetation in Arroyo del Valle is maintaining the groves of sycamore trees, many of which pre-date European presence in the valley. The agencies also seek to enhance valley oak stands within the riparian area, which serves as a wildlife migration corridor.

Balance Hydrologics (Balance) has been retained to assess the current geomorphic conditions of the proposed channel restoration design for Reach-B on Arroyo del Valle, and develop site-specific geomorphic design suggestions that provide fish passage for CCCST and maximize project longevity in this dynamic system subject to many hydrologic and geomorphic influences. Specific objectives of this memo are to:

Describe and assess the existing geomorphic conditions of Reach-B on Arroyo del Valle, and adjacent reaches which may influence the reach geomorphology,

Develop a qualitative assessment of channel stability for the current proposed channel restoration design on Reach-B, and

Provide suggestions for a conceptual channel design of a low-flow channel for Reach-B on Arroyo del Valle.

Project Site Description

The CEMEX Eliot Facility is located in the Livermore-Amador Valley between the cities of Pleasanton and Livermore, California (Figure 1). Arroyo del Valle is located in the Upper Alameda Creek watershed and drains an area of approximately 172 square miles above Reach-B. Arroyo del Valle discharges to Arroyo de la Laguna west of Pleasanton and then flows south and discharges into Alameda Creek near the town of Sunol. Alameda Creek then flows west through the East Bay Hills before discharging into San Francisco Bay.

Arroyo del Valle is regulated by Del Valle Dam which controls 145.8 sq-mi (84.8%) of the total watershed above Reach-B on the project site (Foged, 2014b). The watershed above Del Valle Dam is



comprised of steep-sloped canyons composed primarily of hard sedimentary and metasedimentary rocks with small areas of basic igneous rocks (Welch et al., 1961).

The CEMEX Eliot Facility Site is located just downstream of Sycamore Grove Park. Arroyo del Valle flows along the southern portion of the Eliot Facility adjacent to Lakes A and B (Figures 2 and 3). The arroyo flows through two small lakes along the south side of the Shadow Cliffs Regional Recreation Area and then continues west through the city of Pleasanton. Several small streams drain into Arroyo del Valle between Del Valle Dam and Arroyo de la Laguna. Reach-B on Arroyo del Valle runs from the Isabel Avenue overpass downstream (west) approximately 4,450 feet. It is bound by Vineyard Avenue on the south, Isabel Avenue on the east, and the levee for Lake B on the north.

Preliminary Geomorphic Assessment

The project site is an active gravel mine with several open gravel pits. Reach-B of Arroyo del Valle is situated between Lake B on the CEMEX Eliot facility to the north, and Vineyard Avenue to the south (Figure 2). Gravel extraction along Reach-B has historically occurred in relict stream channels and Holocene alluvium (Qhfp). The geology of the Project site and surrounding vicinity is shown on maps by Helley and Graymer (1997). Gravel mining on Reach-B has been dormant for at least 40 years and currently occurs outside of and to the north of Reach-B.

Field Data Collection

Our analysis utilized a field-based approach to evaluate channel roughness based on particle size distributions collected via pebble counts along Reach-B on Arroyo del Valle. The approach was to identify a minimum of six (6) locations with riffle morphology throughout Reach-B on Arroyo del Valle based on site access and perform a pebble count at each location. Pebble counts provide particle size distributions from which channel roughness can be estimated. Senior Geomorphologist Bill Christner, PhD and Staff Geomorphologist Chelsea Neill visited the site to make measurements on October 7, 2015. After an initial visual survey of Reach-B from the Isabel Avenue overpass downstream approximately 6,500-feet, it became apparent the channel proper was impenetrable due to thick vegetation throughout the riparian corridor. Furthermore, vegetative growth throughout Reach-B was so extensive it encroached well in to the active channel and was now the dominant control on channel roughness throughout Reach-B.

We were able to gain access to the channel at two locations, ADV-01 and ADV-02 (Figure 2). Channel geometry data were estimated at both sites with a field tape and pebble count data of the bed-surface material were collected. Channel substrate at both sites was covered with a veneer of silt- and clay-sized mixed with organics.

Reach-B, Arroyo del Valle

ADV-01 was the furthest downstream site sampled and is interpreted as a river crossing. Data were collected immediately upstream of the crossing, but results are influenced by the presence of the crossing. Channel geometry data were estimated with a field tape and a pebble count was performed just upstream of the crossing within the active channel (Figures 3 and 4).



ADV-02 was located approximately 2,150-feet upstream from ADV-01. The site was difficult to access and heavily influenced by encroaching woody riparian vegetation into the active channel. Channel geometry data were estimated with a field tape and a pebble count was performed across the active channel (Figures 3 and 4).

ADV-01a was located off-channel on channel right (north), and is interpreted as a relict, abandoned channel formed under pre-dam hydrologic conditions. Pebble count data were collected here (Figure 4).

Due to the limited accessibility of Arroyo del Valle throughout Reach-B, coupled with the vegetative control on roughness, an alternative approach to field data collection was proposed. After review of aerial images of Arroyo del Valle, and discussion with Brown and Caldwell, it was decided to access Arroyo del Valle in Sycamore Grove Park (see below).

Reach-A, Arroyo del Valle

The stream channel corridor was explored, and three (3) sites on Reach-A were assessed on October 22, 2015 by Bill Christner, PhD, and Eric Donaldson, PG; ADV-A1, ADV-A2, and ADV-A3 (Figure 5). Sites were selected based on accessibility, and evaluated based on observations up and downstream of each section. Channel geometry data were estimated with a field tape. No pebble counts were performed but channel substrate was visually assessed (Figure 6).

Sycamore Grove Park (SGP), Arroyo del Valle

We visited Sycamore Grove Park (SGP) on October 8, 2015. The park is located immediately upstream of the CEMEX Eliot facility, east of Vallecitos Road (Figure 7). The park is part of the Livermore Area Park and Recreation District (LAPRD). Arroyo del Valle flows east-to-west through the park with walking trails set back from both banks. A bridge crosses Arroyo del Valle at the lower end just before it flows out of the park. There are two wet crossings approximately 0.5 (Olivina Trail Crossing) and 1.0 (Kingfisher Crossing) miles upstream of the foot bridge. A South Bay Aqueduct Discharge pipe is located on the left bank immediately downstream of the Kingfisher (uppermost) Crossing (Figure 7). We estimated a discharge of 10 cfs from the pipe, which, at the time of the visit, appeared to be the sole source of flow in Arroyo del Valle through the project reach.

SGP contains relict, braided channel morphology, attributed to geomorphic processes that were operating prior to the construction of Del Valle Dam. While multiple channels are present in SGP, flows are presently restricted to a single braid/thread. Channel access was not inhibited by vegetation, and vegetation did not appear to influence channel roughness and morphology when compared to Reaches A and B. After performing an initial visual survey of Arroyo del Valle in SGP, we identified four (4) sites for data collection (Figure 7) which included channel geometry, particle size distributions, and slope. Data at ADV-SGP-01 through ADV-SGP-03 were collected at riffles, and ADV-SGP-04 data were collected at a pool (Figures 8, 9, and 10).

Channel Slope and Sinuosity (Preliminary Historical Map Review)

Road crossings, current and historic gravel mining, and the heavily altered hydrology and sediment regime are the primary controls on the longitudinal profile of Arroyo del Valle. We noted two potential areas of channel destabilization during our field investigation. One at the transition from Reach-A to



Reach-B at the Isabel Avenue over-pass. The other along the lower section of Arroyo del Valle in SGP, just upstream of the footbridge.

The area between Reach-A and Reach-B (Isabel Avenue) appears to be recently armored with rip-rap and forms a convex shaped slope as it transitions from Reach-A to Reach-B. The convex slope is evident in the longitudinal profile developed by WRECO for its HEC-RAS modeling of the proposed bridge expansion on State Route 84 (Liang, 2009). Vegetation throughout the site has been removed, including several trees along the channel banks, allowing easy access to the channel on both banks. Rip-rap extends from the lower portion of Reach-A, under the Isabel Avenue bridge, into the upper portion of Reach-B, and covers approximately 420-feet of channel bank-to-bank.

Another area of channel destabilization can be viewed in SGP from the lower pedestrian bridge immediately south of the parking lot off Wetmore Road. The right bank has a vertical exposure of 12 – 15 feet above the channel bottom. The area of channel destabilization is not armored and begins approximately 120 feet downstream of the pedestrian bridge and continues upstream for 450-feet (+/-).

These two areas of potential channel destabilization on Arroyo del Valle may indicate the channel is in a state of disequilibrium and may still be adjusting to hydrologic changes or land-use changes within the watershed including: the operations of Del Valle Dam, historical gravel mining activities, and urbanization. A March-2006 bridge inspection report by Caltrans noted that Arroyo del Valle, between Reach-A and Reach-B, had degraded (incised) 5.9-feet from 1983 to 1999 (Caltrans, 2006, in Liang, 2009). The report noted the incision was due to in-stream gravel mining. Caltrans noted that since 1999 the channel had stabilized and they assumed negligible channel bed incision during that time period. However, Caltrans HQ has declared the existing Isabel Avenue bridge scour critical and noted that the existing rock slope protection (RSP) alone is insufficient for scour protection for the new piers when the Isabel Avenue bridge is widened (Liang, 2009) and will likely be replaced. It is reasonable to assume that the grade control at Isabel Avenue will remain stable and the risk of knick-point migration upstream into Reach A, and associated transient sediment pulse is minimal.

We reviewed the 1953 USGS 7.5-minute quadrangle for Livermore, California to assess flow patterns and slope on Arroyo del Valle prior to construction of Del Valle Dam1. We assessed Arroyo del Valle from elevation 360-feet above sea level (fasl) upstream to 500-fasl (Figure 11). This included an area from just west of the present-day CEMEX Eliot Facility, upstream to just below the present day Del Valle Dam. Channel sinuosity of the current single-thread channel on Arroyo del Valle between these elevations is 1.06 ft/ft.

We also looked at the historical slope on Arroyo del Valle to develop slope estimates prior to the construction of Del Valle Dam. Slope estimates for each reach are presented in Table 1.

1 Future work should include review of more detailed topographic data, possibly including the 2006 county-wide LiDAR dataset.



Table 1. Slope values on Arroyo del Valle estimated from the 1953 USGS Quadrangle for Livermore, California.

Reach Downstream Elevation Upstream Elevation Slope

Reach-B 400 407 0.0020

Reach-A 407 445 0.0054

Sycamore Grove Park 445 500 0.0046

Overall 360 500 0.0051

Downstream of Reach-B 360 400 0.0080

Hydrology

Sub-Watershed Peak Flows

Field evidence of channel-forming flows are confounded by the complex hydrologic history of Arroyo del Valle. Flows in Arroyo del Valle are regulated by releases from Del Valle Dam and inputs from the South Bay Aqueduct. In order to develop a conceptual restoration design for Arroyo del Valle through Reach-B, information regarding the bankfull, or channel-forming flow is desired.

Del Valle Reservoir has altered the hydrologic flow regime in Arroyo del Valle (Figure 12). The impact of the dam on flows in Arroyo del Valle is most evident by examining the pre- and post-dam peak flow records. The maximum post-dam peak flow of 2,980 cfs is less than the mean pre-dam peak flow of 3,075 cfs. Additionally, the minimum peak flow pre-dam is 0.5 cfs, while minimum post-dam peak flows are 8.6, which corresponds closely with the average daily release from Del Valle Dam of 10 cfs.

Current flows in Arroyo del Valle are due to releases from Del Valle Dam and inputs from the South Bay Aqueduct. In order to develop a conceptual restoration design for Arroyo del Valle through Reach-B, information regarding the bankfull, or channel forming flow is desired. Bankfull or channel-forming flows are generally associated with the 1.5 to 2-year recurrence interval. In an attempt to develop an understanding of the hydrologic regime for Arroyo del Valle we obtained flow estimates for various recurrence intervals from multiple sources, each source utilizing a different methodology. Estimates from the various methods provide reasonable bracketing for the 2-year recurrence interval for Reach-B on Arroyo del Valle.

A detailed analysis of Arroyo del Valle hydrology, just upstream of the project site at Sycamore Grove Park (SGP), was developed by Kamman Hydrology and Engineering, Inc., for the SGP management plan (Kamman, 2009). This work provides an estimated peak flow for the estimated 1.5-year through 500-year recurrence intervals. Flood flows were also developed by the Federal Emergency Management Agency (FEMA) which provides peak flow estimates for the 10-, 50-, 100- and 500-year recurrence intervals. Rantz’s regional equations for the San Francisco Bay Region provide peak flow estimates for the 2-, 5-,



10-, 25- and 50-year recurrence intervals (Rantz, 1973). And USGS regional equations establish for the California Central Coast hydrologic region provide peak flow estimates for the 2-, 5-, 10-, 25-, 50-, and 100-year recurrence intervals (Gotvald et al., 2012; Jennings et al., 1993). Results from all four methods are presented in Table 2.

Table 2. USGS peak discharge estimates for Arroyo del Valle based on USGS methods, regional equations and FEMA flood insurance studies.

Recurrence USGS FEMA Kamman and others, 2009

Rantz, 1973

Interval Peak flow (cfs) Peak flow (cfs) Peak flow (cfs) Peak flow (cfs)

2-year 509 NA 222 290

5-year 1,207 NA 1,077 1,101

10-year 1,750 1,860 2,385 1,884

25-year 2,504 NA 5,435 2,852

50-year 3,102 4,150 9,137 4,460

100-year 3,738 7,000 14,460 NA

200-year 4,349 NA NA NA

500-year 5,187 9,080 NA NA

Note: A watershed size of 26.2 square miles (below Del Valle Dam) was used for the estimates we developed using USGS procedures.

Hydraulic Geometry

Hydraulic geometry is used to describe the natural channel geometry that form as a result of the interaction of many factors including climate, land development, sediment sources and transport, bank stability, and riparian assemblage.

Bankfull relations need to be applied loosely, with due deference for the changes that come with time in an evolving landscape, particularly those heavily affected by anthropogenic modifications. Since Del Valle Dam was constructed in 1968, peak flows have diminished and summer flows increased. Arroyo del Valle is likely still adjusting to the upstream construction of Del Valle Dam, and impacts due to urbanization, gravel mining, and other land-use changes. Similarly, channels adjust naturally to episodic events, such as watershed-scale wildfires and floods. Shrub encroachment into Reach-B is likely a result of sustained summer releases from Del Valle Dam; under drier pre-dam conditions, the impenetrable growth might not have developed. Given this dynamism, there is no absolute ‘correct value’ for computing an appropriate set of bankfull dimensions for Arroyo del Valle, nor should there be. The design objective should be to initially place the stream within an acceptable range of geometries to allow adjustment with time and within the flow and sediment regime it will experience.



The primary source for our investigation into appropriate hydraulic geometry for Reach-B on Arroyo del Valle came from data collected in SGP, supplemented with pebble count data collected in Reach-B. We measured channel geometry at four (4) sites on Arroyo del Valle in SGP. Data collection included channel cross-sections, one longitudinal profile, and particle size distributions via pebble counts. Table 3 presents bankfull relations for Arroyo del Valle based on data collected in SGP. We used these relationships to assist in the development of conceptual channel design for Reach-B.

Table 3. Preliminary bankfull hydraulic geometry values for Arroyo del Valle in Sycamore Grove Park reflecting the 2-year recurrence interval under the regulated flow regime.

Unregulated drainage area,

26.2 square miles

Threshold Grain Size

(mm) Bankfull Width (ft) Mean Bankfull

Depth (ft) Bankfull XS

Area (ft2) Width-to-

Depth Ratio

ADV-SGP-01 67 31.0 1.6 48.1 20

ADV-SGP-02 61 33.7 1.5 49.4 23

ADV-SGP-03 49 48.6 1.2 58.8 40

ADV-SGP-04 51 44.2 1.3 56.0 35

Note: Threshold grain size estimates based on a measured slope of 0.0102 (1.02 %).

Conceptual Channel Design Analysis and Suggestions

Project Design Criteria

Preliminary conceptual geomorphic and biologic design goals for Reach-B on Arroyo del Valle include the following:

Develop a stable channel corridor geometry that will adjust naturally, but neither aggrade nor degrade grossly over time,

Support sediment transport, albeit diminished by the presence of the dam,

Allow the bankfull channel to be occupied for flows above 10 cfs,

Convey flood flows,

Provide functional passage for CCCST, and

Provide functional habitat to establish native plant communities.

We understand the design team has established the following preliminary conceptual channel design criteria specific for Reach-B on Arroyo del Valle:

Total floodplain width not to exceed 260-feet.



Upstream tie-in at station 53+50 with channel invert elevation at 390 feet above sea level (fasl).

Downstream tie-in at station 9+00 with channel invert elevation at 370 fasl.

Channel and floodplain slope not to exceed 0.045 percent (.0045).

Convey the FEMA 100-year flow without overtopping channel levees along Lake B.

Channel geometry (width. depth, slope and sinuosity) to provide sediment transport at the dominant ‘sediment transporting discharge.’

Our review of the existing proposed channel design was based on these criteria. The proposed channel restoration design provides a 10-ft wide x 2-ft deep low channel within a 200-ft wide flood channel bordered by 3:1 side slopes 10-ft high (Figure 13). As part of the existing proposed design, the right bank forms a levee between the restored channel corridor on Reach-B and Lake B. The top of the levee is 30-ft wide with a 2 % slope towards Reach-B. Under this existing proposed design, longitudinal slope is not to exceed 0.45 %, and channel roughness was set at 0.045 for the low-flow channel and 0.080 for the flood channel. We reviewed the channel geometry of the existing proposed restoration design for Reach-B on Arroyo del Valle as presented in the Reclamation Plan Amendment (Spinardi, 2013). In addition to this review, we utilized River4m software to analyze all geomorphic data for Arroyo del Valle (Mecklenburg, 1999). The software uses methods established by the USDA (Harrelson, Rawlins and Potyondy, 1994). The software provides evaluation tools to:

Plot cross-sectional and longitudinal survey data,

Calculate basic hydraulic characteristics at various flow depths,

Calculate channel geometry and entrenchment, and

Calculate and plot particle size distributions from pebble counts and estimate channel roughness and threshold grain size2.

Low-Flow Channel

Our analysis suggests that the proposed low-flow channel slope of 0.45 % with Manning’s roughness of 0.045 will result in an entrenched channel with a flow depth of 0.6 feet and velocity of 1.5 fps at a discharge of 10 cfs (Figure 14). Shear stress at the 10 cfs discharge is estimated to be 0.16 (lbs/sq-ft) with a threshold grain size of 10 mm. The proposed low-flow channel design has the capacity to mobilize medium sized gravel and smaller material (≤ 10 mm) at the average daily flow release of 10 cfs.

River4m suggests that at the maximum flow depth of 2-ft, the proposed low-flow channel will convey up to 56 cfs with a velocity of 2.8 fps. Estimated shear stress and threshold grain size increase to 0.40 (lbs/sq-ft) and 24 mm respectively, and indicate the channel has the capacity to mobilize sediment slightly less than the average D50 of 28 mm measured in SGP and ADV-01a in Reach-B (Figures 4 and 10). While the erosive forces associated with the average daily flow of 10 cfs are relatively stable, the

2 Threshold grain size is the particle predicted to be at the threshold of motion.



entrenched nature of the proposed design confines all flows up to 56 cfs within the 10-ft wide low-flow channel resulting in higher shear stresses and mobilizing particles approaching the measured D50. High flows in the proposed low-flow channel will produce erosive forces that will re-work channel materials in the bed and banks. This is an unstable condition and will ultimately produce a new channel geometry for the low-flow channel that may not allow for steelhead passage.

Preliminary review suggests that one option to avoid the anticipated instability in the low-flow channel is to reduce channel slope by increasing sinuosity. This will lower shear stresses throughout the flow capacity in the low-flow channel. However, it may result in sediment deposition and ultimately channel erosion as the low-flow channel readjusts.

The suggested approach here would be to 1) reduce channel slope by increasing sinuosity, and 2) redesign the low-flow channel to incorporate relaxed (laid-back) banks so that as flow depths increase, channel velocity and their associated shear forces will remain relatively minimal (small). Figure 15 illustrates a suggested alternative cross-section at two flow stages. The alternative design incorporates a smaller cross-sectional area, more channel variability, and a reduced channel slope of 0.0040 (0.40 percent).

Flow stage in the top view (A) is 10 cfs with a water depth of 0.7 ft, velocity of 1.6 fps, shear stress of 0.30 lbs/sq-ft, and a threshold grain size of 10 mm. Flow stage in the bottom view (B) is at the top-of-bank with a discharge of 17 cfs, water depth of 0.9-ft, velocity of 1.9 fps, and a threshold grain size of 12 mm. The geometric and hydraulic values are similar for this cross-section at both stages. This suggests the channel has the capacity to transport material between ≤ 12 mm without adverse effects on channel geometry through a range of flow stages in the low-flow channel. Neither cross-section is entrenched with ER3 values of 11 at 10 cfs, and 15 at 17 cfs. The lack of entrenchment is interpreted as a relatively stable channel design for the low-flow channel.

The low-flow channel will include site-appropriate riparian vegetation and habitat features to promote fish passage for CCST.

Intermediate Channel aka: Bankfull Channel

The proposed channel restoration design incorporates a large floodplain, approximately 95-ft wide on both sides above the top elevation of the low-flow channel (Figure 13). This design approach results in shallow flows across the floodplain for flows above the low-flow discharge. The incorporation of an intermediate channel (aka: bankfull channel) into the proposed restoration channel design will allow for the development of habitat features between the low-flow channel and the bankfull channel.

Typically, the bankfull channel is associated with the 1.5-yr to 2.0-year return flow in a natural (i.e. unregulated) system. While flows in Arroyo del Valle are controlled by Del Valle Dam, the 26.2 sq-mi watershed below the dam does provide some unregulated flow to the system. As mentioned earlier, we have reviewed the post-dam hydrology for the site and developed an estimate of 256 cfs for the 2-year return flow. We use the term “bankfull” here to signify this 2-year flow of 256 cfs.

3 Entrenchment is the vertical containment of a river. It is defined as the channel width at two times the bankfull depth divided by the bankfull width.



Analysis of the existing proposed design for the estimated bankfull discharge of 256 cfs results in shallow waters on the floodplain with a maximum water depth of 3.8-ft occurring only in the location of the low-flow channel. Water depths on the floodplain range from 1.8-ft near the low-flow channel, and diminish to zero at the furthest extent of the flow. The restoration design would benefit from the incorporation of an intermediate channel configuration that would accommodate the bankfull flow (2-year return flow). Overbank flows above the low-flow channel allow fish access to floodplains where they are able to seek velocity refuge. However, flows depths of 1.8-feet and less offer little habitat for fish and warrant an alternative approach to the channel design (Myrick and Cech, 2004, Hampton, Payne, and Thomas, 1997). We suggest an alternative design approach that incorporates an intermediate channel geometry based on a bankfull flow of 256 cfs, that incorporates habitat features such as woody riparian structures which force deep pools, backwater areas, and side-channels. The 256 cfs estimate is the average of the Kamman and Rantz bankfull estimates (Table 2). The USGS bankfull estimate was not considered in this estimate because it not designed for small watersheds. Developing a detailed bankfull design is beyond the scope of the current effort, but we do provide one potential conceptual alternative design cross-section in Figure 16.

This conceptual design is based on a slope 0.45 % with channel roughness of 0.045, and incorporates the conceptual low-flow channel. Maximum depth at the bankfull elevation is 3.5-ft with water depths of 2.0-ft on both sides of the low-flow channel. Maximum channel velocity is 2.9 fps with a shear stress of 0.43 lbs/sq-ft and a threshold grain size of 26 mm. Channel width is 57 ft with a cross-sectional area of 88-sq-ft. We suggest a design approach that incorporates an intermediate channel with a meander sinuosity slightly less than the low-flow channel. Intermediate channel geometry may include pools and possible off channel, backwater areas for aquatic habitat.

Single Thread or Braided Channel Morphology

Leopold and Wolman developed a relationship of bankfull discharge and channel slope for braided and non-braided streams (Leopold and Wolman, 1957). The proposed combination of a 256 cfs bankfull discharge with a 0.0045 slope plots in the vicinity of the line separating the two geomorphic channel types. It is unclear at this time whether the channel design for Reach-B on Arroyo del Valle should be a single thread or multichannel design due to the lack of information regarding slope, and the current trajectories of the channel in response the geomorphic influences on the reach discussed earlier (changed hydrology, urbanization, etc.). While the Leopold/Wolman data were developed for natural, unregulated systems, they do provide a good starting point in the design process, and as mentioned earlier, knowledge of the appropriate slope value is lacking at this stage in the design. It is also worth noting that identifying the correct type of system is very important. A restoration project on Uvas Creek on a reach similar to Arroyo del Valle, in nearby Santa Clara County failed shortly after restoration was completed (Kondolf et al., 2001). The failed restoration on Uvas Creek shares many similarities with Arroyo del Valle, most notably:

Regulated system,

Historically braided,

Historic gravel mining, and



Single thread channel restoration design.

The authors also noted that the bankfull discharge and observed slope for Uvas Creek plotted in the transition area between braided and meandering channels. The design incorporated a single-thread channel that failed during runoff flows with a return period of 5-6 years (Kondolf et al., 2001).

Geomorphic conditions on Reach-B of Arroyo del Valle are evolving in response to changes in hydrology (ephemeral to perennial flows) and sediment loading. Future work on Arroyo del Valle should include a careful assessment of the changing flow and sediment regime in Arroyo del Valle, including the recent channel design plus any available monitoring data from Reach A.

Conclusions

CEMEX seeks to mine, restore and reclaim Reach-B on Arroyo del Valle on its Eliot Facility in Pleasanton, California. The site occupies a significant portion of the riparian corridor between the dam and Arroyo del Valle’s confluence with Arroyo de la Laguna, the master natural drain for the Livermore Valley that conveys flows to Alameda Creek and ultimately San Francisco Bay. This technical memo is limited to recommendations for the configuration of a low-flow channel on Reach-B designed to convey 10 cfs, the average daily flow for Arroyo del Valle.

The existing proposed channel design for Reach-B on Arroyo del Valle incorporates a 20 sq-ft low-flow channel within a 200-ft wide flood channel with a slope of 0.0045 (0.45 %). The existing proposed geometry for the low-flow channel has a maximum discharge capacity of 56 cfs with a velocity of 2.5 fps. The low-flow channel should be designed to convey the average daily discharge of 10 cfs. The existing proposed configuration creates entrenched conditions within the low-flow channel with the potential to erode channel material up to 24 mm which may result in unstable conditions and prevent passage for CCST.

Preliminary analysis of the discharge record on Arroyo del Valle suggests the low-flow channel should be inset within an intermediate bankfull channel, capable of conveying approximately 256 cfs. At 256 cfs, the stream should have the competence to transport bed material in the range of 25 to 30 millimeters (1 to 1.2 inches). Substantial portions of the current bed material fall within this range or smaller, and should enable rejuvenation of the future bed surface. Channel reconstruction material should be sized to exceed the estimated threshold grain size of the reconstructed channel.

We propose the development of a two-stage channel within the larger 200-ft wide flood corridor that incorporates a more naturalized low-flow channel within a larger bankfull channel, sized to accommodate the 2-year return flow of 256 cfs. This two-stage design alternative provides a low-flow channel sized to accommodate the average daily flow of 10 cfs at a velocity of 1.6 fps, with a capacity of 17 cfs at a velocity of 1.9 fps. Computed estimates of threshold grain size are 10 mm at 10 cfs, and 12 mm at 17 cfs. This proposed, two-stage geomorphic channel design alternative will accommodate the expected daily flow of 10 cfs within a larger channel designed to convey the 2-year flow of 256 cfs.

Currently it is uncertain whether the channel configuration should be single thread or braided. Our preliminary review of the channel history and geomorphology suggests that channel restoration for



Reach-B on Arroyo del Valle may be suited to a single thread channel. However, the proposed restoration channel design specifications for Reach-B are on the threshold between a braided and single thread morphology, highlighting the need for further background work to help define the appropriate channel slope and identify potential sources of sediment which may destabilize the proposed channel design. Ultimately, careful consideration of the system evolution and watershed processes in Arroyo del Valle will provide the background necessary to understand the channel processes controlling channel form. This in turn will benefit the project and lead to a design that allows for natural sediment transport and bedform development while improving fish passage and minimizing impacts to adjacent infrastructure.

Completion of Del Valle Reservoir in 1968 strongly altered the fundamental flow and sediment transport functions of Arroyo del Valle downstream of the dam. These changes appear to be in the early stages of transition and manifestation in the channel morphology on Arroyo del Valle. Channel restoration projects on systems with changed (reduced) runoff and sediment loads involve the careful prediction of channel form and dimensions suitable to the altered conditions (Kondolf et al., 2001). Therefore, conventional rules-of-thumb, such as setting the bankfull depth at the 1.5- to 2-yr peak flow elevation must be verified before implementation.

Next Steps

Additional work has been identified that will provide insight into channel evolution and sediment transport. This work, listed below, is currently in-progress with field work expected to be completed by August 31, 2016. This includes:

Assess sediment loading from streambank erosion in SGP.

Assess the potential particle size distribution of the material to be used for channel restoration. This will constrain potential channel erosion and assist with establishing channel design criteria.

Assess the particle size distribution of the material in the channel splay in Reach-B. This will provide insight into sediment transport dynamics at various flows.

Review of historical aerial photography and recent LiDAR data to better constrain channel dynamics and future trajectory.

Limitations

This work was executed to the standard of care in Northern California for preliminary stable channel design. It is important to note that stream-enhancement design science is inherently inexact. Realistically, the design concepts presented are a first step towards a stable channel design that incorporates CCCST habitat and native plants from riparian through transitional to upland habitat.

Qualitative and quantitative analyses of pre- and post-restorations through the western states have revealed what many people also intuitively know: the nature of creeks and rivers is not strictly predictable – they are dynamic systems. Adjustments may be warranted in the future as more becomes known about the likely response of Arroyo del Valle to flows within its unregulated watershed, including episodic events and how these will evolve with a changing climate.



This document is not intended to be a Design Basis Report (DBR), which Balance typically develops as part of the engineering design process. We assume a Design Basis Report will be completed at a later stage as the restoration design moves forward. Use of this report as a sole basis for restoration or construction inherently bypasses several important steps in the design and review process. Such use may harm, rather than enhance local channel conditions.

As the restoration design moves forward the Design Team has the resources and expertise to develop two-dimensional models and evaluate both CCCST habitat and potential levee scour. Results of this exercise will provide qualitative estimates and increase the confidence in the final channel design. Similarly, infiltration into the adjoining basins may require further analysis in order to meet the goals of the general and natural-resource plans discussed above.

Closing

This geomorphic and hydraulic assessment is presented to facilitate evaluation of the proposed restoration design for Reach-B on Arroyo del Valle. We look forward to working with the design team (Team) and all relevant stakeholders (agency representatives, Zone-7, Alameda County) to move forward with the conceptual designs presented here for this important and worthwhile project. If you have any questions, feel free to contact us.

Sincerely, BALANCE HYDROLOGICS, INC. ________________________________________ Bill Christner, Ph.D. Project Geomorphologist - Project Manager ________________________________________ Eric Donaldson, P.G. Project Geomorphologist __________________________for Barry Hetch__ Barry Hecht, C.E.G., C.Hg. Principal Geomorphologist

Enclosures: Figures 1-16



References

California Regional Water Quality Control Board, 1986. Water quality control plan: San Francisco Bay Basin (Region 2), revised January – 2007. California Agencies. Paper 393. http://digitalcommons.law.ggu.edu/caldocs_agencies/393.

Fisher, H., Brown, E.G., and Warne, W.E., 1963. Bulletin No. 13, Alameda county investigation. A report by the State of California Department of Water Resources. March, 1963.

Foged, N, 2014. Hydraulic modeling of Arroyo del Valle. Technical memorandum 1, prepared for CEMEX Construction Materials, Inc. February 12, 2014.

Foged, N, 2014b. Arroyo del Valle diversion and conveyance feasibility. Technical memorandum 2, prepared for CEMEX Construction Materials, Inc. March 7, 2014.

Govald, A. J., N. A. Barth, A. G. Veilleux, and C. Parrett. 2012. Methods for determining magnitude and frequency of floods in California, based on data through water year 2006: U.S. Geological Survey Scientific Investigations Report 2012 - 5113.

Hampton, M., Payne, T.R., and Thomas, J.A., 1997. Microhabitat suitability criteria for anadromous salmonids of the Trinity River. U.S. Department of Interior, Fish and Wildlife Service, Coastal California Fish and Wildlife Office, Arcata, California.

Harrelson, C.C, Rawlins, C.L., and Potyondy, J.P., 1994. Stream channel reference sites: An illustrated guide to field technique. General Technical Report RM-245. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 61 p.

Helley, E.J., and Graymer, R.W., 1997. Quaternary geology of Alameda County, and parts of Contra Costa, Santa Clara, San Mateo, San Francisco, Stanislaus, and San Joaquin Counties, California: A digital database. U.S. Geological Survey Open-File Report 97-97.

Jennings, M.E., Thomas, W.O., and Riggs, H.C., 1993. Nationwide summary of U.S. Geological Survey regional regression equations for estimating magnitude and frequency of floods for ungaged sites, 1993. USGS Water-Resources Investigations Report 94-4002.

Kamman Hydrology & Environmental Engineering, Inc. (Kamman), 2009. Phase 2 Technical Report, Sycamore Grove Recovery Program, Sycamore Grove Park, Livermore, California. Prepared for Livermore Area Recreation and Park District 4444 East Avenue, Livermore, California 94550 and the Zone 7 Water Agency 100 North Canyons Parkway, Livermore, California 94551. Edited by Kamman Hydrology & Engineering, Inc., 7 Mt. Lassen Drive, Suite B250, San Rafael, California 94903.

Kane, W.F, 2013. CEMEX Eliot Quarry, Lakes A and B slope stability investigation, Alameda County, California. Project No. GT13-16. Consulting report prepared for CEMEX Construction Materials by Kane Geo Tech Inc.

Kondolf, G.M., Smeltzer, M.W., and Railsback, S.F., 2001. Design and performance of a channel reconstruction project in a coastal California gravel-bed stream. Environmental Management 28:6, pp 761-776.



Kopania, A., 2013. Hydrology and water quality analysis report, Lake A and Lake B expansion, CEMEX Eliot Quarry – SMP-23, Pleasanton, California. Report prepared by EMKO Environmental, Inc.

Leopold, L.B. and Wolman, M.G., 1957. River channel patterns: braided, meandering, and straight. United States Geological Survey Professional Paper 282-B.

Liang, Han-Bin, 2009. Bridge Design Hydraulic Study Report for the State Route 84 Expressway Widening Project, Cities of Livermore and Pleasanton, Alameda County, California. Consulting report prepared for Caltrans and Alameda County Transportation Improvement Authority by WRECO, May-2009.

Marren, P. M., Grove, J. R., Webb, J. A., and Stewardson, M. J., 2014. The potential for dams to impact lowland meandering river floodplain geomorphology. The Scientific World Journal, 2014, 309673. http://doi.org/10.1155/2014/309673.

Mecklenburg, D.E., 1999. The reference reach spreadsheet, v2.2 L. Ohio Department of Natural Resources.

Myrick C.A., Cech J.J., 2004. Temperature effects on juvenile anadromous salmonids in California's central valley: What don't we know? Reviews in Fish Biology and Fisheries, v14: p113–123.

Rantz, S.E., 1973. Suggested criteria for hydrologic design of storm-drainage facilities in the San Francisco Bay Region, California. United States Geological Society Open-File Report 71-341.

Spinardi Associates, 2013. Reclamation plan amendment, CEMEX application for a Reclamation Plan Amendment, Eliot Facility – SMP-23, California Mine 91-01-0009. Consulting report prepared for CEMEX Construction Materials. June – 2013.

Waananen, A. O., and Crippen, J.R., 1977. Magnitude and frequency of floods in California: U.S. Geological Survey Water-Resources Investigations Report 77 - 21.

Welch, L.E., Huff, R.C., Dierking, R.A., Cook, T.D., Bates, L.A., and Andrews, W.F., 1961. Soil survey of the Alameda area, California. United States Department of Agriculture, Soil Conservation Service, in cooperation with the California Agricultural Experiment Station.



FIGURES

© 2015 Balance Hydrologics, Inc.Source: Google Maps

Figure 1. Location of Reach-B and Reach-A on Arroyo del Valle, CEMEX Eliot Facility, Pleasanton, California.

215101 Tech_Memo_Figures.pptx

Chain of Lakes

Reach-B

Reach-A

Arroyo de la Laguna

© 2015 Balance Hydrologics, Inc.Source: Google Earth

Figure 2. Reach-B on Arroyo del Valle, CEMEX Eliot Facility, Pleasanton, California indicating location of data collection sites ADV-01, ADV-02, and ADV-01a. Dashed red line represents 4,450 foot reach length. Solid yellow polygon is rough approximation of study site.


ADV-01

ADV-02

ADV-01a

© 2015 Balance Hydrologics, Inc.

Figure 3. Cross-sections ADV-01 and ADV-02 on Reach-B, Arroyo del Valle, CEMEX Eliot Facility, Pleasanton, California. Solid blue line indicates approximate observed water surface elevation. Dashed green lines indicate extent of vegetative encroachment into the channel. 215101 Tech_Memo_Figures.pptx

Limit of Vegetative Encroachment


Figure 4. Cumulative particle size distribution for Reach-B, Arroyo del Valle, CEMEX Eliot Facility, Pleasanton, California.



Figure 5. Reach-A on Arroyo del Valle, CEMEX Eliot Facility, Pleasanton, California indicating data observation sites ADV-A1 thru ADV-A3. Dashed red line represents Arroyo del Valle. Solid yellow polygon is rough approximation of CEMEX property around Lake-A.


ADV-A1

ADV-A2

ADV-A3


Figure 6. Cross-sections ADV-A1. ADV-A2, and ADV-A3 on Reach-A, Arroyo del Valle, Pleasanton, California. Solid blue line indicates approximate observed water surface elevation Dashed green lines indicate extent of vegetative encroachment into the channel.


Limit of Vegetative

Encroachment

Limit of Vegetative

Encroachment

Limit of Vegetative

Encroachment

Limit of Vegetative

Encroachment


Figure 7. Location of Arroyo del Valle, Sycamore Grove Park, Pleasanton, California indicating data collection sites ADV-SGP-01 thru ADV-SGP-04. Dashed red line represents Arroyo del Valle. Solid yellow polygon is rough approximation of Sycamore Grove Park.


ADV-SGP-02

ADV-SGP-03

ADV-SGP-01

ADV-SGP-04

Kingfisher Crossing

South Bay Aqueduct Discharge

Pipe


Figure 8. Cross-sections ADV-SGP-01 and ADV-SGP-02 on Arroyo del Valle in Sycamore Grove Park, Pleasanton, California. Solid blue line indicates the elevation of the 2-year return flow (256 cfs).

214163 Aerial photos.pptx


Figure 9. Cross-sections ADV-SGP-03 and ADV-SGP-04 on Arroyo del Valle in Sycamore Grove Park, Pleasanton, California. Solid blue line indicates the elevation of the 2-year return flow (256 cfs).

214163 Aerial photos.pptx


Figure 10. Individual and cumulative particle size distributions for ADV-SGP-01 through ADV-SGP-04 on Arroyo del Valle, Sycamore Grove Park, Pleasanton, California.



Figure 11. Longitudinal profile of Arroyo del Valle as taken from the 1953 USGS Quadrangle, Livermore, California. Dashed red line represents the approximate slope of the proposed restoration channel. Stations begin with the 340‐foot contour.



Figure 12. Annual peak discharge for Arroyo del Valle as measured at USGS gage #11176500, Livermore, California. Red line represents the installation of Del Valle dam in 1968. Blue dashed line is the mean peak discharge pre-dam (3,075 cfs). Brown dashed line is the mean peak discharge post-dam (685 cfs).


Pre-Dam Post-Dam



Figure 13. Proposed restoration design for Reach-B on Arroyo del Valle illustrating the low flow geometry within the larger flood corridor. Image modified from Spinardi, 2013.

215101 Tech_Memo_Figures.pptx © 2015 Balance Hydrologics, Inc.


Source: Google Earth

Figure 14. Proposed cross-sections for Reach-B (A) illustrating the difference in water depths for the low-flow channel at 10 cfs (B) and top-of-bank flow at 56 cfs (C) on Arroyo del Valle, Pleasanton, California. Solid blue line indicates water depth at specified discharge. Note the entrenchment conditions in cross-section B.214163 Aerial photos.pptx

A

B10 cfs

C56 cfs


Figure 15. Proposed cross-sections for Reach-B (A), illustrating the difference in water depths for the low-flow channel at 10 cfs (B), and top-of-bank flow at 17 cfs (C) on Arroyo del Valle, Pleasanton, California. Solid blue line indicates water depth at specified discharge. Note the lack of entrenchment in both cross-sections. 214163 Aerial photos.pptx

A

B10 cfs

C17 cfs


Figure 16. Future proposed restoration design cross-section for Reach-B on Arroyo del Valle (A) illustrating the bankfull geometry that includes the low-flow channel, and accommodates the 2-year recurrence flow of 256 cfs (B), and the estimated elevation of the maximum design flood (FEMA 100-year) flow of 7,000 cfs (C).214163 Aerial photos.pptx

A

C7,000 cfs

B256 cfs

E-1


Appendix E: Field Data

Appendix E Conceptual Design for Arroyo del Valle Realignment at Lake B

E-2 CEMEX AdVR Concept Design 20160718.docx


Conceptual Design for Arroyo del Valle Realignment at Lake B Appendix E

E-3


Figure E-1. Cross-section and bankfull estimate for observation point 1








E-5









E-7


Figure E-10. Bed gradation curves based on Wolman Pebble Counts

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0.0002441

0.0004883

0.0009766

0.0019531

0.0039063

0.0078125

0.015625

0.03125

0.0625

0.125

0.25

0.5

1

2

4

8

16

32

64

128

256

512

1024

2048

4096

Percent Finer by Wieght

Part

icle

Siz

e (m

m)

Obse

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ion

Poin

t 1Ob

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0

Clay

Silt

Sand

Grav

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sBo

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F-1


Appendix F: Infiltration Testing

Appendix F Conceptual Design for Arroyo del Valle Realignment at Lake B

F-2 CEMEX AdVR Concept Design 20160718.docx


216034 Infiltration Memo 05-13-2016 1

BALANCE HYDROLOGICS, Inc. MEMO To: Ron Wilson, CEMEX From: Bill Christner (Balance Hydrologics, Inc.) and Andy Kopania (EMKO

Environmental, Inc.) Date: May 13, 2016 Subject: Infiltration Tests of Native and Spoil Soil Material Along Reach-B,

Arroyo del Valle, CEMEX Eliot Facility This memo presents the results of Balance Hydrologics’ and EMKO’s infiltration tests and analysis of the native and spoil soil material along Reach-B, of Arroyo del Valle on the CEMEX Construction Materials, Inc. (CEMEX) Eliot Facility located between the cities of Pleasanton and Livermore within the unincorporated area of Alameda County, California. CEMEX is seeking the approval of an amendment to its existing Reclamation Plan, which was originally approved in 1987 under Surface Mining Permit 23 (SMP-23).

Alameda County issued a Notice of Preparation of a Draft Environmental Impact Report in 2015 for the Reclamation Plan Amendment in accordance with the California Environmental Quality Act (CEQA). Initial entitlement discussions with agency representatives have prompted CEMEX to conduct investigations and prepare a draft conceptual design document in support of the proposed realignment of Reach-B on Arroyo del Valle.

Preliminary design meetings identified the need for infiltration data on native and spoil soil material. Infiltration data will provide insight into the hydrologic properties of soil materials that may be used for channel reconstruction. Balance and EMKO visited the site on March 28, 2016 to perform the desired tests. This memo describes the test methods and analysis carried out to evaluate the infiltration rates of the native and spoil soil materials.

Goals and Objectives The goal of the infiltration investigation is to evaluate the infiltration rates of native and spoil soil material in terms of their suitability for use as a construction material of the reconstructed channel on Arroyo del Valle. A secondary objective is to provide a quantitative assessment of the potential change in the rate of percolation from the existing stream bed compared to the realigned stream bed, and the qualitative

BALANCE HYDROLOGICS, Inc.


implications for seepage and slope stability along the south slope of the Lake B mining pit.

General Technical Approach and Work Conducted To evaluate the infiltration rates of the soils, field tests were conducted utilizing a dual-ring infiltrometer and methods described by the United States Geological Society (USGS, 1963). Two metal rings are driven into the soil surface (Figure 1) and water is then introduced into both cylinders. Water depths are measured at specified time intervals until a relatively constant rate is achieved. The constant rate of water surface decline (drawdown) in the rings reflects the steady-state infiltration rate.

Infiltration rates are affected by many variables including but not limited to the: soil texture and structure, surface soil condition (compacted), antecedent soil moisture, head of the applied water, depth to ground water, length of time water is applied, biological activity, and atmospheric pressure (Brady and Weil, 1999).

Infiltration tests were performed at four (4) sites, two (2) in native soil material along the riparian corridor of Reach-B, and two (2) on spoil soil material (Figure 2). Native soil test sites represent infiltration rates under existing conditions along Reach-B of Arroyo del Valle. Spoil soil material test sites are intended to be representative of infiltration rates that would occur through the realigned channel bed1. Test times ranged from 20 minutes at the N1 site, to 30 minutes at N2, S1, and S2 sites. Soil antecedent moisture conditions were relatively moist as indicated from nearby precipitation gages. Rainfall totals from two nearby precipitation gages indicate the area received between 0.3 and 0.6 inches of precipitation (Figure 3) in the week prior to the infiltration tests (2016, CDE). Precipitation totals for water year 2016 (WY-2016) vary between 11.40 inches and 15.75 inches since the beginning of the water year (October 1, 2015).

Setting Historically, Arroyo del Valle was an intermittent stream (SEFI, 2013). As the stream exited the confines of the mountains onto the broad valley floor, it lost power and dropped its sediment load forming an alluvial fan with a braided channel network. The braided channel network included broad, nearly level, terraces and floodplains.

1 The realigned channel segment will require cut, fill, and compaction of the spoil soil material present in the areas tested. Thus, existing spoil soil material in the area of the proposed realignment is representative of the soil conditions that will exist as part of the substrate under the realigned channel.



Soils across the Livermore Valley are dominated by the Yolo-Pleasanton association (Westover and Van Duyne, 1910; Welch et al., 1966). Yolo soils are entisols formed in fine-loamy alluvium derived from sedimentary formations. Entisols are soils defined by the absence or near absence of horizons, or layers that clearly reflect soil-forming processes. They are found on nearly level to moderately sloping alluvial fans (Soil Survey Staff, 2016). They tend to be well-drained with slow to medium runoff and moderate permeability.

Pleasanton soils are gravelly fine sandy loam alfisols, and occur on nearly level to gently sloping alluvial fans and terraces. Alfisols typically exhibit well-developed, contrasting soil horizons or layers. They are well-drained soils with slow to medium runoff, and moderately slow permeability (Soil Survey Staff, 2016).

Historical accounts describe the alluvial soils as “river wash” and characterize the streambeds as very porous material, underlain by a bed of coarse gravel several feet thick (Westover and Van Duyne 1910; Welch et al. 1966). Infiltration rates of the coarse channel material often allowed surface flows to percolate into the sediments at a rate such that channel flow was intermittent (SEFI, 2013).

Findings Surface Infiltration Rates Infiltration data for all four (4) sites are presented in Attachment A. Infiltration rates are similar for most sites except the N1 site (Figure 4). Infiltration rates at N1 were much higher than infiltration rates measured at the other sites. Initial infiltration at N1 was 60.0 in/hr and quickly fell to 21.0 in/hr after 8.5 minutes (510 seconds). These rates are significantly higher than infiltration rates observed at the other three (3) sites. Initial infiltration rates at sites N2, S1, and S2 were 15.0 in/hr, 6.0 in/hr, and 15.0 in/hr respectively. These rates fell quickly and stabilized at 3.4 in/hr, 0.59 in/hr, and 1.9 in/hr respectively after 20 minutes (1200 s). Predictive equations for infiltration rates were developed from the field data based on best-fit lines. These equations indicate infiltration rates continue to decline at each site through time (Table 1).



Conclusions and Implications for Design Concerns were raised about the potential for high water seepage rates through the soils used to reconstruct Reach-B on Arroyo del Valle. Infiltration tests were performed at four (4) sites along Reach-B, two (2) on native soil material, and two (2) on spoil soil material. Field test results indicate infiltration rates for the spoil soil material are less (slower) then those observed in native soil materials. Results from this field investigation indicate that infiltration rates following channel reconstruction should be similar to or slower than current rates. Therefore, infiltration of water through the realigned channel of Arroyo del Valle would not steepen the groundwater gradient toward the south edge of Lake B, would not increase the groundwater elevation at the south edge of Lake B, and would not increase the rate of seepage into the south face of Lake B. As such, realignment of Reach-B would not alter the hydrologic conditions along the south side of Lake B in a manner that would be inconsistent with the existing geotechnical slope stability analysis (Kane GeoTech, 2015).

Limitations This report was prepared in general accordance with the accepted standard of practice in surface-water and groundwater hydrology existing in Northern California for projects of similar scale at the time the investigations were performed. No other warranties, expressed or implied, are made.

As is customary, we note that readers should recognize that interpretation and evaluation of subsurface conditions and physical factors affecting the hydrologic

Table 1. Infiltration rates (in/hr) for sites N1, N2, S1, and S2 from 20 minutes through 12 hours times.

Site

Infiltration Rate (in/hr)

20 (mins)

30 (mins)

1 (hr)

12 (hr)

1200 (sec)

1800 (sec)

2600 (sec)

43,200 (sec)

N1 13.47 11.40 8.58 3.09

N2 3.43 3.11 2.62 1.43

S1 0.59 0.46 0.31 0.07

S2 1.91 1.61 1.20 0.42



context of any site is a difficult and inexact art. Judgments leading to conclusions and recommendations are generally made with an incomplete knowledge of the conditions present. More extensive or extended studies, including additional hydrologic baseline monitoring, can reduce the inherent uncertainties associated with such studies. We note, in particular, that many factors affect local and regional groundwater levels, and soil composition varies both spatially and temporally. If the client wishes to further reduce the uncertainty beyond the level associated with this study, Balance should be notified for additional consultation.

We have used standard environmental information such as rainfall, topographic mapping, and soil mapping, in our analyses and approaches without verification or modification, in conformance with local custom. New information or changes in regulatory guidance could influence the plans or recommendations, perhaps fundamentally. As updated information becomes available, the interpretations and recommendations contained in this memo may warrant change. To aid in revisions, we ask that readers or reviewers advise us of new plans, conditions, or data when they become available.

Concepts, findings and interpretations contained in this report are intended for the exclusive use of CEMEX, under the conditions presently prevailing except where noted otherwise. Their use beyond the boundaries of the site could lead to environmental or structural damage, and/or to noncompliance with water-quality policies, regulations or permits. Data developed or used in this report were collected and interpreted solely for developing an understanding of the hydrologic context at the site as an aid to conceptual planning and channel and wetland restoration design. They should not be used for other purposes without great care, updating, review of sampling and analytical methods used, and consultation with Balance staff familiar with the site. In particular, Balance Hydrologics, Inc. should be consulted prior to applying the contents of this report to geotechnical or facility design, routine wetland management, sale or exchange of land, or for other purposes not specifically cited in this report.

Finally, we ask once again that readers who have additional pertinent information, who observed changed conditions, or who may note material errors should contact us with their findings at the earliest possible date, so that timely changes may be made.



References

Brady, N.C., and Weil, R.R., 1999. The nature and properties of soils. Twelfth Edition. Prentice Hall, 881 p.

California Data Exchange Center (CDEC), 2016. California Department of Water Resources. Precipitation data for Calaveras Road (CAD) and Dublin-San Ramon Fire House (DBF) gages. Accessed on 5/4/2016.

California Data Exchange Center (CDEC), 2016. California Department of Water Resources. Precipitation data for Calaveras Road (CAD) and Dublin-San Ramon Fire House (DBF) gages. Accessed on 5/4/2016.

Johnson, A. I., 1963. A field method for measurement of infiltration, general groundwater techniques. U.S. Geological Survey, Water Supply Paper, 1544-F, 27, 1963.

Kane GeoTech, 2015, CEMEX Eliot Quarry Lake B evaluation report, Alameda County, California, 5/7/2015.

San Francisco Estuary Institute (SFEI), 2013. Alameda Creek watershed historical ecology study. February 2013.

Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Official Soil Series Descriptions. Available online. Accessed 11/19/2014.

U.S. Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS), 2015. National soil survey handbook, title 430-VI. Available online. Accessed 11/23/2015.

Welch, L., Huff, R.C., Dierking, R.A., Cook, T.D., Bates, L.A., and Andrews, W.F., 1966. Soil survey of the Alameda area, California. United States Department of Agriculture, Soil Conservation Service, in cooperation with the University of California Agricultural Experiment Station.

Westover, H.L., and Van Duyne, C., 1910. Soil survey of the Livermore area, California. United States Department of Agriculture, Soil Conservation Service.



Attachments

Figure 1. Photos of the dual-ring infiltrometer set-up at site S1 on the CEMEX Eliot Facility, Alameda County, California

Figure 2. Location of infiltration sites on Reach-B along Arroyo del Valle, CEMEX Eliot facility, Alameda County, California

Figure 3. Charts illustrating the accumulated precipitation for the Dublin-San Ramon Fire House gage and the Calaveras Road gage

Figure 4. Infiltration rates at four (4) sites along Reach-B on Arroyo del Valle at the CEMEX Eliot Facility, Alameda County, California.

Appendix A. Summary of Infiltration Tests for Sites: N1, N2, S1, and S2

FIGURES


Figure 1. Photos of the dual-ring infiltrometer set-up at site S1 on the

CEMEX Eliot Facility, Alameda County, California, March

28, 2016.

215184 Protrait_Figs-2.pptx


Figure 2. Location of infiltration sites on Reach-B along Arroyo del Valle (dashed blue line), CEMEX Eliot Facility, Alameda County, California, March 28, 2016. South test sites (S1 and S2) reflect spoil soil material, north test sites (N1 and N2) reflect native soil material. 216034_Lndscp-Figs.pptx

Source: Google Maps


Figure 3. Charts illustrating the accumulated precipitation for the Dublin-San Ramon Fire House (DBF) gage (top) and the Calaveras Road (CAD) gage (bottom) from March 1, 2016 through May 4, 2016. Data obtained from the California Department of Water Resources Data Exchange Center (CDEC). Both gages located within 10 miles of the project site.

215184 Protrait_Figs-2.pptx

216034_Infiltration_Tests

y = 248.32x‐0.411

y = 19.346x‐0.244

y = 37.755x‐0.587

y = 38.536x‐0.424

0

10

20

30

40

50

60

70

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Infiltration Ra

te (in/hr)

Time (s)

Site‐N1

Site‐N2

Site‐S1

Site‐S2

Infiltration rates at four (4) sites: N1 (solid blue line), N2 (dotted green line), S1 (short dashed gold line), and S2 (long dashed red line) along Reach-B on Arroyo del Valle at the CEMEX Eliot Facility, Alameda County, California.

Figure 4

APPENDIX A

Summary of Infiltration Tests for Sites: N1, N2, S1, and S2

Appendix A. Summary of infiltration tests for sites: N1, N2, S1, and S2. CEMEX Eliot Facility, Arroyo del Valle, Alameda County, California

Project Number/Name: 216034_Arroyo del Valle InfiltrationLocation: Site‐N1Date: 28‐Mar‐16

Time Depth Rate Time Depth Rate Time Depth RateObservation (sec) (in) (in/hr) (sec) (cm) (cm/hr) (sec) (inch) (in/hr)

0 0 7.00 NA 0 17.780 NA 0 7.00 NA1 30 6.50 60.0 30 16.510 152.4 30 6.50 60.02 60 6.10 48.0 60 15.494 121.9 60 6.10 48.03 90 5.80 36.0 90 14.732 91.4 90 5.80 36.04 120 5.50 36.0 120 13.970 91.4 120 5.50 36.05 150 5.25 30.0 150 13.335 76.2 150 5.25 30.06 180 5.00 30.0 180 12.700 76.2 180 5.00 30.07 210 4.75 30.0 210 12.065 76.2 210 4.75 30.08 240 4.50 30.0 240 11.430 76.2 240 4.50 30.09 270 4.30 24.0 270 10.922 61.0 270 4.30 24.010 300 4.10 24.0 300 10.414 61.0 300 4.10 24.011 330 3.90 24.0 330 9.906 61.0 330 3.90 24.012 360 3.75 18.0 360 9.525 45.7 360 3.75 18.013 390 3.55 24.0 390 9.017 61.0 390 3.55 24.014 420 3.40 18.0 420 8.636 45.7 420 3.40 18.015 450 3.25 18.0 450 8.255 45.7 450 3.25 18.016 480 3.10 18.0 480 7.874 45.7 480 3.10 18.017 510 2.90 24.0 510 7.366 61.0 510 2.90 24.0181920212223242526272829303132333435363738394041

Location: Site‐N2Date: 28‐Mar‐16

Time Depth Rate Time Depth RateObservation (sec) (in) (in/hr) (sec) (cm) (cm/hr)

0 0 7.10 NA 0 18.0 NA1 30 6.98 15.00 30 17.7 38.102 60 6.90 9.00 60 17.5 22.863 90 6.81 10.80 90 17.3 27.434 120 6.80 1.20 120 17.3 3.055 150 6.75 6.00 150 17.1 15.246 180 6.70 6.00 180 17.0 15.247 240 6.65 3.00 240 16.9 7.628 300 6.55 6.00 300 16.6 15.249 360 6.52 1.80 360 16.6 4.5710 420 6.40 7.20 420 16.3 18.2911 480 6.31 5.40 480 16.0 13.7212 540 6.21 6.00 540 15.8 15.2413 600 6.15 3.60 600 15.6 9.1414 660 6.05 6.00 660 15.4 15.2415 720 6.00 3.00 720 15.2 7.6216 780 5.92 4.80 780 15.0 12.1917 840 5.90 1.20 840 15.0 3.0518 900 5.80 6.00 900 14.7 15.2419 960 5.75 3.00 960 14.6 7.6220 1020 5.69 3.60 1020 14.5 9.1421 1080 5.60 5.40 1080 14.2 13.7222 1140 5.53 4.20 1140 14.0 10.6723 1200 5.46 4.20 1200 13.9 10.67242526272829303132333435363738394041

Location: Site‐S1Date: 28‐Mar‐16


0 0 1.00 NA 0 2.5 NA1 30 0.95 6.00 30 2.4 15.242 60 0.93 2.40 60 2.4 6.103 90 0.91 2.40 90 2.3 6.104 120 0.90 1.20 120 2.3 3.055 180 0.85 3.00 180 2.2 7.626 240 0.80 3.00 240 2.0 7.627 300 0.78 1.20 300 2.0 3.058 360 0.73 3.00 360 1.9 7.629 420 0.71 1.20 420 1.8 3.0510 480 0.70 0.60 480 1.8 1.5211 540 0.69 0.60 540 1.8 1.5212 600 0.68 0.60 600 1.7 1.5213 720 0.61 2.10 720 1.5 5.3314 840 0.60 0.30 840 1.5 0.7615 960 0.58 0.60 960 1.5 1.5216 1080 0.52 1.80 1080 1.3 4.5717 1200 0.51 0.30 1200 1.3 0.7618 1500 0.49 0.24 1500 1.2 0.6119 1800 0.42 0.84 1800 1.1 2.1320212223242526272829303132333435363738394041

Location: Site‐S2Date: 28‐Mar‐16


0 0 2.00 NA 0 5.08 NA1 60 1.75 15.00 60 4.45 38.102 120 1.63 7.20 120 4.14 18.293 180 1.59 2.40 180 4.04 6.104 240 1.51 4.80 240 3.84 12.195 300 1.48 1.80 300 3.76 4.576 360 1.42 3.60 360 3.61 9.147 420 1.40 1.20 420 3.56 3.058 480 1.35 3.00 480 3.43 7.629 540 1.31 2.40 540 3.33 6.1010 600 1.29 1.20 600 3.28 3.0511 660 1.23 3.60 660 3.12 9.1412 720 1.20 1.80 720 3.05 4.5713 840 1.11 2.70 840 2.82 6.8614 900 1.08 1.80 900 2.74 4.5715 1200 0.90 2.16 1200 2.29 5.4916 1500 0.68 2.64 1500 1.73 6.7117 1800 0.41 3.24 1800 1.04 8.23181920212223242526272829303132333435363738394041

G-1


Appendix G: Magnitude-Frequency Analysis

Appendix G Conceptual Design for Arroyo del Valle Realignment at Lake B

G-2 CEMEX AdVR Concept Design 20160718.docx


Conceptual Design for Arroyo del Valle Realignment at Lake B Appendix G

G-3


A Model for Geomorphic Evolution Although observations from catastrophic events often suggest that infrequent events of immense magnitude tend to drive geomorphic processes such as stream channel formation, this is typically not the case. Wolman and Miller described how the geomorphic evolution of landscapes is strongly influenced by the amount of “work” done by forces acting on the system (e.g., shear forces caused by flowing water), and that the relative amount of work done depends not only on the magnitude of the force, but also on the frequency of occurrence (Wolman and Miller 1960).

Figure D-1 is a graphical representation of the “work done” concept, where the frequency of occurrence is log-normally distributed and the magnitude of the influencing force (i.e., applied stress) increases in accordance with a mathematical power function. The product of the frequency of the occurrences and the magnitude of the influencing force is referred to as the “effective work” curve (noted “c” in Figure D-2). The relationship shown in Figure D-2 illustrates how frequent mid-range events do more effective work than extremely large, relatively rare events.

Figure G-1. Relation between applied stress and frequency of occurrence in geomorphic processes

Adapted from Wolman and Miller (1960).

Magnitude-Frequency Analysis Practical application of the effective work concept is sometimes referred to as magnitude-frequency analysis (MFA) (Soar and Thorne 2001). Bledsoe et al. describe MFA as a fundamental tool for fluvial stream assessment (Bledsoe et al. 2007). MFA can be used to define the “effective discharge” for a stream, which is the flow rate corresponding to the maximum work on the effectiveness curve (Bledsoe et al. 2007). The effective discharge is roughly equivalent to the channel-forming (or bankfull) discharge as defined by Leopold et al. (Leopold et al. 1964).

MFA can also be used to define geomorphically significant flows, or the range of flow rates over which a substantial portion of the channel-forming work is done. Leopold et al. describe geomorphically significant flows as the range of flow rates occurring between a lower limit of competence (critical stress necessary for grain movement) and an upper limit at which flow is no longer confined to the channel (i.e., greater than bankfull discharge) (Leopold et al. 1964). Figure D-

Applied Stress

(a)

Rate

of se

dimen

t mov

emen

t(b

)Fr

eque

ncy o

f occ

urre

nce

(c)Pr

oduc

t of fr

eque

ncy a

nd ra

te

(a)

(b)

(c)



2 shows a modified version of the effective work graphic where MFA is used to define geomorphic parameters such as effective discharge and a range of geomorphically significant flows for a stream.

Figure G-2. Schematic representation of MFA results used to define geomorphic parameters

Note that the discharge frequency distribution for a stream (curve “b” in Figure D-1) is developed using a series of discrete discharge bins. The value at each point in the discharge frequency curve represents the amount of time (e.g., hours per year) stream discharges fall within the specified bin range. The size of the bins can be variable as long as the distribution of discharges is adequately represented.

The rate-of-movement curve (curve “a” in Figure D-1) can be calculated by either a sediment transport function or an equivalent work rate function. In either case, the curve represents the rate at which sediment is mobilized for any given stream discharge (higher discharge rates result in greater mobilization for the particle sizes evaluated). Multiplying stream discharge rates by sediment transport rates (or effective work rates) provides results in terms of total sediment load or total effective work (units of mass mobilized or units of work per year). This is represented by curve “c” on Figure D-1.

Computational Considerations The development of flow frequency distribution data requires careful attention because the methods used to prepare these data are of critical importance to MFA evaluations. Flow hydrographs were processed into flow distribution histograms by summing the number of time steps for which stream flow values fall within specified ranges of flows, or discrete flow “bins.” Soar and Thorne provide a detailed discussion on how the number and distribution of flow bins can greatly influence MFA results, thus requiring careful selection, and possibly sensitivity testing, to determine the most appropriate method (Soar and Thorne 2001).

Logarithmically distributed flow bins have an advantage over arithmetically distributed (i.e., evenly spaced) flow bins in that stream flows tend to be log-normally distributed, and a larger number of flow bins in the low flow ranges can great improve the resolution of the distribution. However,

Discharge

(a)

Sedim

ent tr

ansp

ort r

ate or

wor

k rate

(b)

Disc

harg

e fre

quen

cy in

units

of tim

e(c)

Sedim

ent lo

ading

or ef

fectiv

e wor

k(a)

(b)

(c)

ThresholdDischarge

Effective Discharge

Geomorphically Significant Flows

Conceptual Design for Arroyo del Valle Realignment at Lake B Appendix G

G-5


logarithmically distributed flow bins can introduce bias to the estimation of parameters such as effective discharge, as described by Soar and Thorne:

If the discharge interval systematically increases, as in a logarithmic scale, then the resultant sample frequency distribution is incorrectly skewed in the negative direction (or misrepresented by exaggeration). As a direct result, the product of sediment load and frequency will tend to follow a similar trend. This is intuitive because in MFA, the sediment load transported by the mean discharge of a class is multiplied by a frequency corresponding to the probability of falling within that class. This probability increases with class size. With logarithmic class intervals, the systematic increase in the size of class interval with increasing discharge will overestimate the effective discharge. (Soar and Thorne 2001)

However, additional investigations and sensitivity testing found that logarithmically distributed flow bins produced satisfactory results due to the following conditions: • Discharges in Arroyo del Valle and tributaries are fairly stable, which minimizes the potential

error. Soar and Thorne’s exploration of the “misrepresentation error” resulting from the above-described bias found that potential errors are greatest for streams with highly variable flow regimes and least for more stable flow regimes (Soar and Thorne 2001). Examining the standard deviation of the natural logarithm of discharges found that stream flows downstream of Del Valle Reservoir are moderately stable.

• A large number of bins (i.e., 200) could be used while still maintaining a well-defined distribution curve, which reduces approximation error. Increasing the number of flow bins decreases the bin size, improves resolution, and provides improved estimates of geomorphic parameters such as effective discharge. However, if bin sizes are too small, there could be bins with zero records. Soar and Thorne recommends that flow bins be large enough to avoid zero values and maintain a continuous flow distribution curve (Soar and Thorne 2001).

• Arithmetic bins resulted in poor resolution at low discharges. Even with as many as 200 arithmetically distributed flow bins, a substantial portion of flow distribution curves tended to fall within the first one or two bins. Logarithmically distributed flow bins provided additional detail that can be used to examine relative differences resulting from small changes in flow regime.



Appendix G References Bledsoe, B.P. and C.C. Watson. April 2001. “Effects of Urbanization on Channel Stability.” Journal of

the American Water Resources Association; Vol. 37, No. 2, p. 255–270.

Leopold, L.B., M.G. Wolman and J.P. Miller. 1964. Fluvial Processes in Geomorphology. Dover Publications, Inc., New York, 1964.

Soar, P.J. and C.R. Thorne. 2001. Channel Restoration Design for Meandering Rivers. ERDC⁄CHL CR-01-1, 416, Engineer Research and Development Center, U.S. Army Corps of Engineers, Vicksburg, Mississippi.

Wolman, M.G., and J.P. Miller. 1960. “Magnitude and Frequency of Forces in Geomorphic Processes.” Journal of Geology; v. 68, p. 54–74.

Documents

Concept Design for the Arroyo del Valle Realignment at Lake Bnps.acgov.org/nps-assets/docs/npstri.pdf · 172-square-mile Arroyo del Valle basin is located upstream of Del Valle Reservoir,